[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.


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?