Support multiple PCI root bus

[FlyGoat]

As reported by @mintsuki, some Intel Arrow Lake S systems have multiple root buses (i.e 0x00-0x7F, 0x80-0xFF).

SeaBIOS need appropriate hint to probe multiple root buses (romfile "etc/extra-pci-roots").

My current idea is to implement CBFS in csmwrap to pass romfiles, I'm currently exploring the option.