arm64: dts: rockchip: add missing rockchip,grf property to rk356x

This commit fixes the error messages

  rockchip_clk_register_muxgrf: regmap not available
  rockchip_clk_register_branches: failed to register clock clk_ddr1x: -524

during boot by providing the missing rockchip,grf property.
Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Tested-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20210823123911.12095-2-michael.riesch@wolfvision.netSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk356x.dtsi

@@ -233,6 +233,7 @@ cru: clock-controller@fdd20000 {
 		#reset-cells = <1>;
 		assigned-clocks = <&cru PLL_GPLL>, <&pmucru PLL_PPLL>;
 		assigned-clock-rates = <1200000000>, <200000000>;
+		rockchip,grf = <&grf>;
 	};
 
 	i2c0: i2c@fdd40000 {