[AMDGPU] Use WriteSALUDummy for v_div_scale* (#191670)
This uses the new HWWriteRes for v_div_scale*
For an explanation of why we want to do this , see
https://github.com/llvm/llvm-project/pull/190095 . In short, the
scheduler will not try to cover the full latency of the instructions
without this new modelling.
For a clear example of this, see the changes to
llvm/test/CodeGen/AMDGPU/schedmodel-dummywrite.mir in the git log of
this PR.
