This implements support for doing a HW synchronization of the CPU
timebases on SMP G5 machines.

 When the proper clock chips are found on i2c, they are used to stop the
timebase clock source during the synchronization process.  This replaces
the software sync algorithm we used so far and provides slightly more
precise results.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>