Qualcomm Technologies Inc. adreno/snapdragon eDP output

Required properties:
- compatible:
  * "qcom,mdss-edp"
- reg: Physical base address and length of the registers of controller and PLL
- reg-names: The names of register regions. The following regions are required:
  * "edp"
  * "pll_base"
- interrupts: The interrupt signal from the eDP block.
- power-domains: Should be <&mmcc MDSS_GDSC>.
- clocks: device clocks
  See Documentation/devicetree/bindings/clocks/clock-bindings.txt for details.
- clock-names: the following clocks are required:
  * "core_clk"
  * "iface_clk"
  * "mdp_core_clk"
  * "pixel_clk"
  * "link_clk"
- #clock-cells: The value should be 1.
- vdda-supply: phandle to vdda regulator device node
- lvl-vdd-supply: phandle to regulator device node which is used to supply power
  to HPD receiving chip
- panel-en-gpios: GPIO pin to supply power to panel.
- panel-hpd-gpios: GPIO pin used for eDP hpd.


Optional properties:
- interrupt-parent: phandle to the MDP block if the interrupt signal is routed
  through MDP block

Example:
	mdss_edp: qcom,mdss_edp@fd923400 {
			compatible = "qcom,mdss-edp";
			reg-names =
				"edp",
				"pll_base";
			reg =	<0xfd923400 0x700>,
				<0xfd923a00 0xd4>;
			interrupt-parent = <&mdss_mdp>;
			interrupts = <12 0>;
			power-domains = <&mmcc MDSS_GDSC>;
			clock-names =
				"core_clk",
				"pixel_clk",
				"iface_clk",
				"link_clk",
				"mdp_core_clk";
			clocks =
				<&mmcc MDSS_EDPAUX_CLK>,
				<&mmcc MDSS_EDPPIXEL_CLK>,
				<&mmcc MDSS_AHB_CLK>,
				<&mmcc MDSS_EDPLINK_CLK>,
				<&mmcc MDSS_MDP_CLK>;
			#clock-cells = <1>;
			vdda-supply = <&pma8084_l12>;
			lvl-vdd-supply = <&lvl_vreg>;
			panel-en-gpios = <&tlmm 137 0>;
			panel-hpd-gpios = <&tlmm 103 0>;
	};

Add MSM eDP controller documentation
dt-bindings: Add MSM eDP controller documentation

Signed-off-by: Hai Li <e16f2cfe3eeddac6a07d0579fc92925faf1d9f49@codeaurora.org>
Signed-off-by: Rob Clark <915c10c999604870200b6defbe633d857c856ca0@gmail.com>
