efi/libstub/arm64: Use 1:1 mapping of RT services if property table exists

The UEFI spec defines (and deprecates) a misguided and shortlived
memory protection feature that is based on splitting memory regions
covering PE/COFF executables into separate code and data regions,
without annotating them as belonging to the same executable image.
When the OS assigns the virtual addresses of these regions, it may
move them around arbitrarily, without taking into account that the
PE/COFF code sections may contain relative references into the data
sections, which means the relative placement of these segments has
to be preserved or the executable image will be corrupted.

The original workaround on arm64 was to ensure that adjacent regions
of the same type were mapped adjacently in the virtual mapping, but
this requires sorting of the memory map, which we would prefer to
avoid.

Considering that the native physical mapping of the PE/COFF images
does not suffer from this issue, let's preserve it at runtime, and
install it as the virtual mapping as well.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>