[mips][msa] Tidy up

lowerMSABinaryIntr, lowerMSABinaryImmIntr, lowerMSABranchIntr,
and lowerMSAUnaryIntr were trivially small functions. Inlined them into
their callers.

lowerMSASplat now takes its callers SDLoc instead of making a new one.

No functional change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191503 91177308-0d34-0410-b5e6-96231b3b80d8