powerpc/85xx: implement hardware timebase sync

Do hardware timebase sync. Firstly, stop all timebases, and transfer the
timebase value of the boot core to the other core. Finally, start all
timebases.

Only apply to dual-core chips, such as MPC8572, P2020, etc.

Signed-off-by: Zhao Chenhui <chenhui.zhao@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>