Davinci: add support for the ea20 board

This board uses the OMAP-L138 SOM stacked on a
custom baseboard. It supports SPI Flash, Ethernet
with RMII.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>