m68knommu: complete generic time

do_set_rtc() isn't required because the work that is handled is
allready served if read_persistent_clock() & update_persistent_clock()
are implemented and CONFIG_GENERIC_CMOS_UPDATE is. sync_cmos_clock()
looks very familiar :)

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>