Add a missing opcode (SMLSLDX) to BadRegsMulFrm() function.

Add more complete sanity check for LdStFrm instructions where if IBit (Inst{25})
is 1, Inst{4} should be 0.  Otherwise, we should reject the insn as invalid.

rdar://problem/9239347
rdar://problem/9239467

llvm-svn: 128977