dt-bindings: Add binding for img,d5520-vxd for J721E

commit c45b294833fd46b7af4f390ddb8d35979ce11ab1 from
TI Linux SDK PROCESSOR-SDK-LINUX-J721E_07.03.00.05

Add the dt-binding for the img,d5520-vxd node for J721E.

Signed-off-by: Angela Stegmaier <angelabaker@ti.com>
Signed-off-by: Sunita Nadampalli <sunitan@ti.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Sidraya Jayagond <sidraya.bj@ti.com>
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>