phy: rockchip-dp: should be a child device of the GRF

The displayport-phy is fully enclosed in the general register files (GRF).
Therefore as seen from the device-tree it shouldn't be a separate platform-
device but instead a sub-device of the GRF - using the simply-mfd mechanism.

The driver entered the kernel in the current merge-window, so we can still
adapt the binding without needing a fallback, as the binding hasn't been
released with a full kernel yet.

While the edp phy is fully part of the GRF, it doesn't have any separate
register set there, so doesn't get any register-area assigned.

Signed-off-by: Heiko Stuebner <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Yakir Yang <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

Documentation/devicetree/bindings/phy/rockchip-dp-phy.txt

···
 	of memory mapped region.
 - clock-names: from common clock binding:
 	Required elements: "24m"
-- rockchip,grf: phandle to the syscon managing the "general register files"
 - #phy-cells : from the generic PHY bindings, must be 0;
 
 Example:
 
-edp_phy: edp-phy {
-	compatible = "rockchip,rk3288-dp-phy";
-	rockchip,grf = <&grf>;
-	clocks = <&cru SCLK_EDP_24M>;
-	clock-names = "24m";
-	#phy-cells = <0>;
+grf: syscon@ff770000 {
+	compatible = "rockchip,rk3288-grf", "syscon", "simple-mfd";
+
+...
+
+	edp_phy: edp-phy {
+		compatible = "rockchip,rk3288-dp-phy";
+		clocks = <&cru SCLK_EDP_24M>;
+		clock-names = "24m";
+		#phy-cells = <0>;
+	};
 };

drivers/phy/phy-rockchip-dp.c

···
 	if (!np)
 		return -ENODEV;
 
+	if (!dev->parent || !dev->parent->of_node)
+		return -ENODEV;
+
 	dp = devm_kzalloc(dev, sizeof(*dp), GFP_KERNEL);
 	if (IS_ERR(dp))
 		return -ENOMEM;
···
 		return ret;
 	}
 
-	dp->grf = syscon_regmap_lookup_by_phandle(np, "rockchip,grf");
+	dp->grf = syscon_node_to_regmap(dev->parent->of_node);
 	if (IS_ERR(dp->grf)) {
-		dev_err(dev, "rk3288-dp needs rockchip,grf property\n");
+		dev_err(dev, "rk3288-dp needs the General Register Files syscon\n");
 		return PTR_ERR(dp->grf);
 	}