Upstream tech debt: BaseRiscVMmuLib violates PI spec

[andreiw]

PI spec sez:

... the DXE driver that produces the EFI_CPU_ARCH_PROTOCOL must
seed the GCD memory space map with the initial state of the^M
attributes for all the memory regions visible to the processor.

Instead the GCD attrs remain 0, even for regions that get accessible page table mappings.