[mips][microMIPS] Implement SHRA[_R].PH, SHRAV[_R].PH, SHRAV[_R].QB,...

[mips][microMIPS] Implement SHRA[_R].PH, SHRAV[_R].PH, SHRAV[_R].QB, SHRAV_R.W, SHRA_R.W, SHRL.PH, SHRL.QB, SHRLV.PH and SHRLV.QB instructions
Differential Revision: http://reviews.llvm.org/D14010

llvm-svn: 253041