Implement ECAM PCIe access

[FlyGoat]

Some platforms have issue on accessing PCI config space via 0xcf8 & 0xcfc IO ports, we should parse MCFG and use ECAM to access PCI config space whenever possible.

This need to be passed to SeaBIOS via EFI_COMPATIBILITY16_TABLE.PciExpressBase.

[FlyGoat]

WIP: https://github.com/FlyGoat/CSMWrap/tree/mcfg