[llvm] [AMDGPU][True16][MC] Support v_swap_b16. (PR #100442)

[Joe Nash via llvm-commits]

https://github.com/Sisyph approved this pull request.

LGTM. If the VOP3 form is supported, we can add a follow up patch.

https://github.com/llvm/llvm-project/pull/100442