ArmPkg/AArch64Mmu: move page table traversal code to separate function

ArmPkg/AArch64Mmu: move page table traversal code to separate function

Move the page table traversal and splitting logic to a separate function
UpdateRegionMapping() and refactor it slightly so we can reuse it later to
implement non-executable regions, for the stack. This primarly involves
adding a value/mask pair to the function prototype that allows us to flip
arbitrary bits on each block entry as the page tables are traversed.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18586 6f19259b-4bc3-4df7-8a09-765794883524