davinci: Add RTC support for DA8xx/OMAP-L13x SoC's

Add RTC support for the da830/omap-l137 and da850/omap-l138
SoC's by leveraging existing the rtc-omap driver.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>