MIPS: Alchemy: RTC counter clocksource / clockevent support.

Add support for the 32 kHz counter1 (RTC) as clocksource / clockevent
device.  As a nice side effect, this also enables use of the 'wait'
instruction for runtime idle power savings.

If the counters aren't enabled/working properly, fall back on the
cp0 counter clock code.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>