Add RTC DT entries in da850 dts file.

Tested on da850-evm device.
Test Procedure:
$ date 2013.01.28-10:00:00 # usage: date[YYYY.]MM.DD-hh:mm[:ss]
$ hwclock -w
(reset board and check system time)
Signed-off-by: NMrugesh Katepallewar <mrugesh.mk@ti.com>
Signed-off-by: NSekhar Nori <nsekhar@ti.com>