RTC: DaVinci RTC driver

This driver features:

* Alarm support.
* Periodic interrupt by using a timer include into the RTC module.
* The update interrupt is not supported by this RTC module.

This driver was tested on a DM365 EVM by using the rtc-test application
from the Documentation/rtc.txt.

Signed-off-by: Miguel Aguilar <miguel.aguilar@ridgerun.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>