Reharmonize the implementation with the spec.

In particular, I altered the naming of some instruction format fields
as well as the names of instruction formats themselves, all in an attempt
to make the implementation be a more straightforward match of the spec.

This patch mostly changes comments to reflect the new harmonized
reality. The only "code-like" change is the renaming of kFmt3inline
and kFmt3rinline to kFmt35mi and kFmt3rmi (respectively), which is
what they're called in the spec.

Bonus: Added the new extended opcode instruction formats to
InstrUtils.h, though I left them commented out for now.

Change-Id: I0109f361c1e9b6f0308c45e8cda5320e9ad3060c