[mips][microMIPS] Implement LWSP and SWSP instructions

Differential Revision: http://reviews.llvm.org/D6416


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224771 91177308-0d34-0410-b5e6-96231b3b80d8
[Hexagon] Adding unsigned halfword load.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224772 91177308-0d34-0410-b5e6-96231b3b80d8