[ARM][DAG] Revert Disable post-legalization store merge for ARM

Partially reverting enabling of post-legalization store merge
(r319036) for just ARM backend as it is causing incorrect code
in some Thumb2 cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319331 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed