The original sync-r4k did a good job on reducing jitter by determine
the "next time value", but it has a limitation that when synchronization
being performed too many times due to high core count or CPU hotplug,
the timewrap on CPU0 will become unaccpetable.

Rework the mechanism based on latest x86 tsc_sync. (It seems like
the original implementation is based on tsc_sync at that time,
so it's just a refresh.) To improve overall performance.

Tesed on Loongson64, Boston, QEMU.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>