[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

llvm-svn: 193237