ARM: OMAP5: board-generic: Add device tree support

Adding the minimal support for OMAP5 evm board
with device tree.

Reviewed-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>