odroid: add odroid U3/X2 device tree description

This is a standard description for Odroid boards.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Tom Rini <trini@ti.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>