[AMDGPU][MC] Allow VOP3C dpp src1 to be imm or SGPR (#87418)

Allows src1 of VOP3 encoded VOPC to be an SGPR or inline immediate on
GFX1150Plus

The w32 and w64 _e64_dpp assembler only real instructions were unused,
and erroneously constructed in a way that bugged parsing of the new
instructions. They are removed.

This patch is a follow up to PR
https://github.com/llvm/llvm-project/pull/87382