ArmPkg/ArmV7Mmu: fix write-through translation table accesses

ArmPkg/ArmV7Mmu: fix write-through translation table accesses

The definition TTBR_WRITE_THROUGH_NO_ALLOC makes little sense, since
a) its meaning is unclear in the context of TTBRx, since write through
   always implies Read-Allocate and no Write-Allocate
b) its definition equals the definition of TTBR_WRITE_BACK_ALLOC

So instead, rename it to TTBR_WRITE_THROUGH and update the definition
to reflect the name.

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@18893 6f19259b-4bc3-4df7-8a09-765794883524