[AMDGPU] Set SchedRW on real instructions

Coyp SchedRW from pseudos to real instructions so that llvm-mca has
access to it. This is NFC for normal compiler codegen, which schedules
pseudos not real instructions.

Add an llvm-mca test for some high latency double-precision instructions
as a smoke test.

Differential Revision: https://reviews.llvm.org/D99187