Rename callee save enumerators.

And related image method enumerators, macros, etc.
Clean up some entrypoint assembly comments.

This is a follow-up to
    https://android-review.googlesource.com/252348

Test: Run ART test suite on host and Nexus 9.
Bug: 30212852
Change-Id: I2707342d4255c88c547655be83ed97a67e12ae9e