[SystemZ] Add support for missing instructions

Summary:
Add support to allow clang integrated assembler to recognize some
missing instructions, for openssl.

Instructions are:
LM, LMH, LMY, STM, STMH, STMY, ICM, ICMH, ICMY, SLA, SLAK, TML, TMH, EX, EXRL.

Reviewers: uweigand

Subscribers: koriakin, llvm-commits

Differential Revision: http://reviews.llvm.org/D22050

llvm-svn: 274869