On integrating LoongArch EDK2 firmware into QEMU build process

[WANG Xuerui]

Hi,

Recently there are reportedly increased general interest in trying out 
LoongArch on top of QEMU, among both end users and organizations; and 
the EDK2 firmware port is fully upstreamed since the stable202211 
version, and a build suitable for QEMU is already possible with 
Platform/Loongson/LoongArchQemuPkg in edk2-platforms. I think providing 
pre-built LoongArch firmware would make it much easier to dabble in 
system emulation, helping those users. (They currently have to pull a 
blob from yangxiaojuan/qemu-binary, and remember to pair certain version 
of QEMU with certain revision of the firmware blob. I'm also one of the 
users who can't remember which version to use, but I can always build my 
own; imagine the difficulty an end user would face!)

So I tried to add a LoongArch build to the list stored in roms/, but 
discovered that edk2-platforms seems not included, because all other 
platforms' EDK2 packages are directly under the main edk2 repo.

The question is: is integrating a platform package from edk2-platforms 
okay under the current build system, so we can arrange to provide 
edk2-platforms also as a submodule and go ahead? Or do we (the LoongArch 
firmware community) have to change the code organization to make 
necessary parts available in the main edk2 repo?

CC-ing target/loongarch maintainers from Loongson too as you may have 
more information.