arm: dts: add U-Boot dtbs for the am625-lp-sk

Add the U-Boot device tree overrides for the am62x-lp-sk reference
board.

Signed-off-by: Nitin Yadav <n-yadav@ti.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>