ArmPkg/ArmV7Mmu: handle memory regions over 4 GB correctly

The ARM_MEMORY_REGION_DESCRIPTOR array provided by the platform may
contain entries that extend beyond the 4 GB boundary, above which
we can't map anything on 32-bit ARM. If this is the case, map only
the 1:1 addressable part.

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@18900 6f19259b-4bc3-4df7-8a09-765794883524