ppc/p4080: Handle timebase enabling and frequency reporting

On CoreNet style platforms the timebase frequency is the bus frequency
defined by 16 (on PQ3 it is divide by 8).  Also on the CoreNet platforms
the core not longer controls the enabling of the timebase.  We now need
to enable the boot core's timebase via CCSR register writes.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>