[PowerPC] A fix for D159073. Do not optimize when register classes are different in src and dst.

For example:
```
  %298:g8rc = RLDICL %297:g8rc, 0, 48
  %299:gprc = COPY killed %298.sub_32:g8rc
  dead %498:gprc = ANDI_rec killed %299:gprc, 1, implicit-def dead $cr0, implicit-def $cr0gt
```