MIPS: DS1286: New RTC driver

This driver replaces the broken DS1286 driver in drivers/char and gives back
RTC support for SGI IP22 and IP28 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>