[0/5 PATCH/RFC PPC64] Initial Power8 keyword support

Five patches to add support for the power8/pwr8 keyword. The changes
are mostly straightforward.
The PPCScheduleP8.td file within a subsequent patch is currently
incomplete. At the moment it is a copy/paste/tweak of the Power7
version. Updates to that file are at the front of the todo line, but
not baked yet.

Thanks,
-Will

In general, please send appropriate patches to the appropriate list
(cfe or llvm). Also patches should go to the -commits list - could
you resend them there? One at a time perhaps?

-eric