da830: Move common code out of da830evm.c file

TI's DA850/OMAP-L138 platform is similar to DA830/OMAP-L137
in many aspects. So instead of repeating the same code in
multiple files, move the common code to a different file
and call those functions from the respective da830/da850
files.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Acked-by: Nick Thompson <nick.thompson@ge.com>
Acked-by: Ben Gardiner <bengardiner@nanometrics.ca>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>