Give a reason for UIO_010

[jhauser-us]

The Architecture Review Committee would like the BRS document to include some non-normative justification for UIO_010, which obligates the UEFI firmware to initialize all PCIe root complexes.

[ved-rivos]

The non-normative justification slightly hints at the fact that this is a stronger requirement than PCI BIOS envisioned. It will be useful to augment that justification to state why PCIe resource allocation and host bridge configurations are not really standardized across platforms and without the firmware initializing the root complexes it may lead to unexpected behaviors.

[andreiw]

@jhauser-us please take a look at #207

[avpatel]

The commit f967ab2 addresses this issue hence closing it.