[mips][msa] Non-constant BUILD_VECTOR's should be expanded to INSERT_VECTOR_ELT instead of memory operations.

The resulting code is the same length, but doesnt cause memory traffic or latency.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191297 91177308-0d34-0410-b5e6-96231b3b80d8