arm64: dts: rockchip: add rockchip,grf property for RK3399 PMUCRU/CRU

The structure rockchip_clk_provider needs to refer the GRF regmap
in somewhere, if the CRU node has not "rockchip,grf" property,
calling syscon_regmap_lookup_by_phandle will return an invalid GRF
regmap, and the MUXGRF type clock will be not supported.

Therefore, we need to add them.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>