ArmPkg/ArmMmuLib: AARCH64: add support for modifying only permissions

ArmPkg/ArmMmuLib: AARCH64: add support for modifying only permissions

Since the new DXE page protection for PE/COFF images may invoke
EFI_CPU_ARCH_PROTOCOL.SetMemoryAttributes() with only permission
attributes set, add support for this in the AARCH64 MMU code.

Move the EFI_MEMORY_CACHETYPE_MASK macro to a shared location between
CpuDxe and ArmMmuLib so we don't have to introduce yet another
definition.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>