[PowerPC] move ctrloop pass before tail duplication

Tail duplication may modify the loop to a "non-canonical" form
that CTR Loop pass can not recognize. We fixed one issue in D135846.
And we found in some other case, the loop is changed to irreducible form.
It is hard to fix this case in CTR loop pass, instead we reorder the
CTR loop pass before tail duplication pass and just after finalize-isel
pass to avoid any unexpected change to the loop form.

Reviewed By: lkail

Differential Revision: https://reviews.llvm.org/D138265