[mips][msa] Added support for matching splat.[bhw] from normal IR (i.e. not intrinsics)

splat.d is implemented but this subtest is currently disabled. This is because
it is difficult to match the appropriate IR on MIPS32. There is a patch under
review that should help with this so I hope to enable the subtest soon.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193680 91177308-0d34-0410-b5e6-96231b3b80d8