[AArch64] Add store + add folding regression tests for the load/store optimization pass.

Add tests for the following transform:

 str X, [x0, #32]
  ...
 add x0, x0, #32
  ->
 str X, [x0, #32]!

with X being either w1, x1, s0, d0 or q0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209627 91177308-0d34-0410-b5e6-96231b3b80d8