[llvm] [MIPS] int <-> `half` conversions with `+msa` (PR #201897)

[Folkert de Vries via llvm-commits]

folkertdev wrote:

It's only a partial fix for https://github.com/llvm/llvm-project/issues/202808, the "Call operand #0 has unhandled type f16" part has not been fixed yet.

https://github.com/llvm/llvm-project/pull/201897