ARM: dts: rockchip: add rga node for rk322x

Add a node to define the presence of RGA, a 2D raster graphic
acceleration unit.

Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
Link: https://lore.kernel.org/r/20200419125134.29923-2-justin.swartz@risingedge.co.za


Signed-off-by: Heiko Stuebner <heiko@sntech.de>