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>

drivers/rtc/Kconfig

@@ -669,6 +669,17 @@ config RTC_DRV_PPC
 	 the RTC. This exposes that functionality through the generic RTC
 	 class.
 
+config RTC_DRV_PXA
+       tristate "PXA27x/PXA3xx"
+       depends on ARCH_PXA
+       help
+         If you say Y here you will get access to the real time clock
+         built into your PXA27x or PXA3xx CPU.
+
+         This RTC driver uses PXA RTC registers available since pxa27x
+         series (RDxR, RYxR) instead of legacy RCNR, RTAR.
+
+
 config RTC_DRV_SUN4V
 	bool "SUN4V Hypervisor RTC"
 	depends on SPARC64