[mips][msa] Implemented fill.d intrinsic.

This intrinsic is lowered into an equivalent BUILD_VECTOR which is further
lowered into a sequence of insert.w's on MIPS32.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191519 91177308-0d34-0410-b5e6-96231b3b80d8