AArch64: Cleanup CCMP code; NFC

Cleanup CCMP pattern matching code in preparation for review/bugfix:
- Rename `isConjunctionDisjunctionTree()` to `canEmitConjunction()`
  (it won't accept arbitrary disjunctions and is really about whether we
   can transform the subtree into a conjunction that we can emit).
- Rename `emitConjunctionDisjunctionTree()` to `emitConjunction()`

llvm-svn: 346203