ARM: dts: rockchip: drop unneeded properties from mipi node

The mipi controller node does contain an unused reg property as well as
unnecessary #address-cells and #size-cells properties for subnodes
not using addresses, so remove those to also make dtc happy.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Rob Herring <robh@kernel.org>