ArmPkg/CpuDxe: ARM: ignore page table updates that only change permissions

ArmPkg/CpuDxe: ARM: ignore page table updates that only change permissions

Currently, we have not implemented support on 32-bit ARM for managing
permission bits in the page tables. Since the new DXE page protection
for PE/COFF images may invoke EFI_CPU_ARCH_PROTOCOL.SetMemoryAttributes()
with only permission attributes set, let's simply ignore those for now.

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