ArmPkg/ArmLib MMU: add functions to set/clear RO and XN bits on regions

ArmPkg/ArmLib MMU: add functions to set/clear RO and XN bits on regions

Use the refactored UpdateRegionMapping () to traverse the translation
tables, splitting block entries along the way if required, and apply
a mask + or on each to set or clear the PXN/UXN/XN or RO bits.

For now, the 32-bit ARM versions remain unimplemented.

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@18587 6f19259b-4bc3-4df7-8a09-765794883524