rtc: driver for pxa27x and pxa3xx SoC

With PXA27x and above, a new RTC hardware block was added in addition to
the legacy one which is also found on the SA1100 SOC family.  This second
RTC block is called "wristwatch" and "periodic interrupt" and works
independently from the other RTC block.

The driver offers provides :
 - a 1Hz ticking clock
 - a periodic alarm, in the 1Hz to 1000Hz range
 - a one shot alarm

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>