[llvm] PPC: Move definitions of predicates with features (PR #157058)

[Lei Huang via llvm-commits]

https://github.com/lei137 commented:

Was there a specific reason you moved these within the section documented as `CPU Directives` vs moving this to just after that section and right before the section labeled:
```
500 //===----------------------------------------------------------------------===//
501 // Classes used for relation maps.
502 //===----------------------------------------------------------------------===//
```

https://github.com/llvm/llvm-project/pull/157058