ArmPkg/ArmMmuLib: remove bogus alignment of page allocations

ArmPkg/ArmMmuLib: remove bogus alignment of page allocations

In commit 7d189f99d81c ("ArmPkg/Mmu: Fix bug of aligning new allocated
page table"), we fixed a flaw in the logic regarding alignment of newly
allocated translation table pages. However, we all failed to spot that
aligning page based allocations to page size is rather pointless to
begin with, so simply allocate a single page each time we add new pages
to the translation tables.

Also, drop the unnecessary cast.

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