ppc/pnv: Move timebase state into PnvCore

ppc/pnv: Move timebase state into PnvCore

The timebase state machine is per per-core state and can be driven
by any thread in the core. It is currently implemented as a hack
where the state is in a CPU structure and only thread 0's state is
accessed by the chiptod, which limits programming the timebase
side of the state machine to thread 0 of a core.

Move the state out into PnvCore and share it among all threads.

Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>