davinci: Add support for DA850/OMAP-L138 EVM board

Add support for the DA850/OMAP-L138 Evaluation Module (EVM)
from TI.  The EVM has User Interface (UI) card which contains
various devices. This UI card can be connected to the base
board. Support for all the devices on the UI card and ones on
the EVM will be added in subsequent patches.

The EVM schematics are not available publicly yet; but should
be available soon.

A new defconfig for this board has been added mainly because
the DA830/OMAP-L137 defconfig forces writethrough cache mode
which is not required on DA850/OMAP-L138.

This patch has been boot tested on DA850/OMAP-L138 EVM
using ramdisk as filesystem.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>