Add BOARD_CUSTOM_BOOTIMG_MK support

This is a combination of 2 commits.
This is the 1st commit message:

    Add BOARD_CUSTOM_BOOTIMG_MK support

    Simplified version of the previous implementation. Recovery's ramdisk
    is spun off from the main recovery target again to allow overriding
    just the image-generation step

    [mikeioannina]: Squash cm-13.0 changes and adapt to N

    Change-Id: I058d214f0cf2d05b7621b369ef1f8a983c3ac258

This is the commit message #2:

    build: Handle custom boot images properly

    When a pre-built image should be used, it should be stored in the
    target files zip so that it can be used with external signing
    processes.

    Original-Change-Id: I2661af9ac58af30bb9314b552775046d3abf44e0
    Change-Id: I10b3bd0bb33489b8ffb26d16d002f8dd6ff405ad

[aleasto]
  Rewritten for R, where the recovery ramdisk is created via
  make dependencies, rather than $(call)s

Change-Id: I058d214f0cf2d05b7621b369ef1f8a983c3ac258

core/Makefile

@@ -1249,6 +1249,8 @@ INTERNAL_MKBOOTIMG_VERSION_ARGS := \
 ifdef BUILDING_BOOT_IMAGE
 INSTALLED_BOOTIMAGE_TARGET := $(BUILT_BOOTIMAGE_TARGET)
 
+ifndef BOARD_CUSTOM_BOOTIMG_MK
+
 ifeq ($(TARGET_BOOTIMAGE_USE_EXT2),true)
 $(error TARGET_BOOTIMAGE_USE_EXT2 is not supported anymore)
 
@@ -1319,6 +1321,7 @@ bootimage-nodeps: $(MKBOOTIMG)
 	$(hide) $(call assert-max-image-size,$(INSTALLED_BOOTIMAGE_TARGET),$(BOARD_BOOTIMAGE_PARTITION_SIZE))
 
 endif # TARGET_BOOTIMAGE_USE_EXT2
+endif # BOARD_CUSTOM_BOOTIMG_MK not defined
 endif # BUILDING_BOOT_IMAGE
 
 else # TARGET_NO_KERNEL == "true"
@@ -1928,6 +1931,7 @@ IGNORE_RECOVERY_SEPOLICY := $(patsubst $(TARGET_RECOVERY_OUT)/%,--exclude=/%,$(r
 
 recovery_kernel := $(INSTALLED_KERNEL_TARGET) # same as a non-recovery system
 recovery_ramdisk := $(PRODUCT_OUT)/ramdisk-recovery.img
+recovery_uncompressed_ramdisk := $(PRODUCT_OUT)/ramdisk-recovery.cpio
 recovery_resources_common := $(call include-path-for, recovery)/res
 
 # Set recovery_density to a density bucket based on TARGET_SCREEN_DENSITY, PRODUCT_AAPT_PREF_CONFIG,
@@ -2191,7 +2195,7 @@ ifndef BOARD_RECOVERY_MKBOOTIMG_ARGS
   BOARD_RECOVERY_MKBOOTIMG_ARGS := $(BOARD_MKBOOTIMG_ARGS)
 endif
 
-$(recovery_ramdisk): $(MKBOOTFS) $(COMPRESSION_COMMAND_DEPS) \
+$(recovery_uncompressed_ramdisk): $(MKBOOTFS) \
 	    $(INTERNAL_ROOT_FILES) \
 	    $(INSTALLED_RAMDISK_TARGET) \
 	    $(INTERNAL_RECOVERYIMAGE_FILES) \
@@ -2226,7 +2230,13 @@ $(recovery_ramdisk): $(MKBOOTFS) $(COMPRESSION_COMMAND_DEPS) \
 	  cp -f $(recovery_wipe) $(TARGET_RECOVERY_ROOT_OUT)/system/etc/recovery.wipe)
 	ln -sf prop.default $(TARGET_RECOVERY_ROOT_OUT)/default.prop
 	$(BOARD_RECOVERY_IMAGE_PREPARE)
-	$(MKBOOTFS) -d $(TARGET_OUT) $(TARGET_RECOVERY_ROOT_OUT) | $(COMPRESSION_COMMAND) > $(recovery_ramdisk)
+	@echo ----- Making uncompressed recovery ramdisk ------
+	$(MKBOOTFS) $(TARGET_RECOVERY_ROOT_OUT) > $@
+
+$(recovery_ramdisk): $(recovery_uncompressed_ramdisk) $(COMPRESSION_COMMAND_DEPS)
+	@echo ----- Making compressed recovery ramdisk ------
+	$(COMPRESSION_COMMAND) < $(recovery_uncompressed_ramdisk) > $@
+
 
 # $(1): output file
 # $(2): kernel file
@@ -2285,8 +2295,12 @@ $(INSTALLED_BOOTIMAGE_TARGET): $(recoveryimage-deps)
 	$(call build-recoveryimage-target, $@, $(PRODUCT_OUT)/$(subst .img,,$(subst boot,kernel,$(notdir $@))))
 endif # BOARD_USES_RECOVERY_AS_BOOT
 
+ifndef BOARD_CUSTOM_BOOTIMG_MK
 $(INSTALLED_RECOVERYIMAGE_TARGET): $(recoveryimage-deps)
 	$(call build-recoveryimage-target, $@, $(recovery_kernel))
+else
+INTERNAL_RECOVERYIMAGE_ARGS += --kernel $(recovery_kernel)
+endif # BOARD_CUSTOM_BOOTIMG_MK
 
 ifdef RECOVERY_RESOURCE_ZIP
 $(RECOVERY_RESOURCE_ZIP): $(INSTALLED_RECOVERYIMAGE_TARGET) | $(ZIPTIME)
@@ -2315,6 +2329,11 @@ ifneq ($(BOARD_NAND_SPARE_SIZE),)
 $(error MTD device is no longer supported and thus BOARD_NAND_SPARE_SIZE is deprecated.)
 endif
 
+ifdef BOARD_CUSTOM_BOOTIMG_MK
+include $(BOARD_CUSTOM_BOOTIMG_MK)
+endif
+
+
 ifneq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
 # -----------------------------------------------------------------
 # the debug ramdisk, which is the original ramdisk plus additional
@@ -4707,6 +4726,12 @@ ifdef BOARD_KERNEL_PAGESIZE
 endif
 	echo "$(INTERNAL_KERNEL_CMDLINE)" > $(zip_root)/VENDOR_BOOT/vendor_cmdline
 endif # INSTALLED_VENDOR_BOOTIMAGE_TARGET
+ifdef BOARD_CUSTOM_BOOTIMG
+	@# Prebuilt boot images
+	$(hide) mkdir -p $(zip_root)/BOOTABLE_IMAGES
+	$(hide) $(ACP) $(INSTALLED_BOOTIMAGE_TARGET) $(zip_root)/BOOTABLE_IMAGES/
+	$(hide) $(ACP) $(INSTALLED_RECOVERYIMAGE_TARGET) $(zip_root)/BOOTABLE_IMAGES/
+endif
 ifdef BUILDING_SYSTEM_IMAGE
 	@# Contents of the system image
 	$(hide) $(call package_files-copy-root, \