[Hexagon] Adding indexed stores.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225005 91177308-0d34-0410-b5e6-96231b3b80d8
[Hexagon] Adding indexed store of immediates.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225006 91177308-0d34-0410-b5e6-96231b3b80d8