RTC: M48T35: new RTC driver

This driver replaces the broken ip27-rtc driver in drivers/char and
gives back RTC support for SGI IP27 machines.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Acked-by: Alessandro Zummo <alessandro.zummo@towertech.it>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>