[POWERPC] 8xxx: MDS board RTC fixes

Now the rtc class ds1374 driver has been added, remove the old rtc
driver hookup code, add rtc node to device trees, and turn on the
new driver in the defconfigs.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>