[PowerPC][NFC] Move codegen tests to PowerPC from MIR/PowerPC

All tests with -run-pass !=none should not in MIR/, See MIR/README.

```
Tests for codegen passes should NOT be here but in
test/CodeGen/sometarget. As
a rule of thumb this directory should only contain tests using
'llc -run-pass none'.
```

llvm-svn: 371857