arm64: dts: rockchip: rk3399: set dummy_cpll and dummy_vpll as fixed clk

to fix up :
[    0.000000] clk: couldn't get clock 4 for /clock-controller@ff760000
[    0.000000] rockchip_clk_of_add_provider: could not register clk provider
The cause of the error:
struct clk *__clk_create_clk(struct clk_hw *hw, const char *dev_id,
			     const char *con_id, bool with_orphans)
{
	/* This is to allow this function to be chained to others */
	if (!hw || IS_ERR(hw))
		return (struct clk *) hw;

	if (hw->core->orphan && !with_orphans)
		return ERR_PTR(-EPROBE_DEFER);

	return clk_hw_create_clk(hw, dev_id, con_id);
}
if clk is orphan and not have the with_orphans flag, it will
register clk provider failed.

Change-Id: I87ca9ec087611a5425545bfc857b09d8438218b5
Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>

arch/arm64/boot/dts/rockchip/rk3399.dtsi

@@ -201,6 +201,20 @@
 		#clock-cells = <0>;
 	};
 
+	dummy_cpll: dummy_cpll {
+		compatible = "fixed-clock";
+		clock-frequency = <0>;
+		clock-output-names = "dummy_cpll";
+		#clock-cells = <0>;
+	};
+
+	dummy_vpll: dummy_vpll {
+		compatible = "fixed-clock";
+		clock-frequency = <0>;
+		clock-output-names = "dummy_vpll";
+		#clock-cells = <0>;
+	};
+
 	amba: bus {
 		compatible = "simple-bus";
 		#address-cells = <2>;