[mips][msa] Add intrinsics that map to pseudo-instructions.

Unlike the previously added intrinsics, these do not map to a single instruction
on MIPS32. They are provided for regularity (to round out the .[bhw] variants
of the same operation) and compatibility with GCC.

Includes:
  copy_[us].d, fill.d, insert.d, insve.d



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193237 91177308-0d34-0410-b5e6-96231b3b80d8