Investigate forcing loading images below 4GiB if available

[andreiw]

As part of developing MultiArchUefiPkg we've seen UEFI apps (thankfully not drivers...yet) that are not 64-bit clean:

• Treating stack (ESP) as 32-bit
• Corrupting AllocatePool pointers to be non-64-bit clean

This appears on a system where UEFI prefers memory > 4GiB. MultiArchUefiPkg already tries putting the emulated stack below 4GiB if possible, and with #5 could also try keeping pool/page allocations below 4GiB as well.

For consistency, it could be interesting if the images themselves were loaded below 4GiB if that were available, i.e. if the whole emulated image handling by DXE supported taking a hint and then reloading the image. Maybe, just try loading the image first below 4GiB regardless if the image type is x64. This could be an EDK2 patch...