ArmPkg/Mmu: Fix literal number left shift bug

ArmPkg/Mmu: Fix literal number left shift bug

There is a hidden bug for below code:

(1 << BaseAddressAlignment) & *BlockEntrySize

From disassembly code, we can see the literal number 1 will be treated
as INT32 by compiler by default, and we'll get 0xFFFFFFFF80000000 when
BaseAddressAlignment is equal to 31. So we will always get 31 when
alignment is larger than 31.

    if ((1 << BaseAddressAlignment) & *BlockEntrySize) {
5224: f9404be0  ldr x0, [sp,#144]
5228: 2a0003e1  mov w1, w0
522c: 52800020  mov w0, #0x1                    // #1
5230: 1ac12000  lsl w0, w0, w1
5234: 93407c01  sxtw  x1, w0

The bug can be replayed on QEMU AARCH64; by adding some debug print,
we can see lots of level 1 tables created (for block of 1GB) even
when the region is large enough to use 512GB block size.

Use LowBitSet64() in BaseLib instead to fix the bug.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18423 6f19259b-4bc3-4df7-8a09-765794883524