[mips][microMIPS] Implement MUL[_S].PH, MULEQ_S.W.PHL, MULEQ_S.W.PHR,...

[mips][microMIPS] Implement MUL[_S].PH, MULEQ_S.W.PHL, MULEQ_S.W.PHR, MULEU_S.PH.QBL, MULEU_S.PH.QBR, MULQ_RS.PH, MULQ_RS.W, MULQ_S.PH and MULQ_S.W instructions
Differential Revision: http://reviews.llvm.org/D14280

llvm-svn: 253651