[FastISel][AArch64] Fold 'AND' instruction during the address computation.

[FastISel][AArch64] Fold 'AND' instruction during the address computation.

The 'AND' instruction could be used to mask out the lower 32 bits of a register.
If this is done inside an address computation we might be able to fold the
instruction into the memory instruction itself.

and  x1, x1, #0xffffffff   ---> ldrb x0, [x0, w1, uxtw]
ldrb x0, [x0, x1]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218030 91177308-0d34-0410-b5e6-96231b3b80d8