[mips][msa] Float vector constants cannot use ldi.[wd] directly. Bitcast from the appropriate integer vector type.

Fixes an instruction selection failure detected by llvm-stress.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195444 91177308-0d34-0410-b5e6-96231b3b80d8