ARM: DTS: omap3-u-boot.dtsi

Create generic omap3-u-boot.dtsi file that omap3 based boards
can include to generate device tree in SPL for booting MLO.

Credit should go to Tom Rini.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Tested-by: Derald D. Woods <woods.technical@gmail.com>