Device-Tree bindings for drm hdmi driver

Required properties:
- compatible: value should be one among the following:
	1) "samsung,exynos4210-hdmi"
	2) "samsung,exynos4212-hdmi"
	3) "samsung,exynos5420-hdmi"
- reg: physical base address of the hdmi and length of memory mapped
	region.
- interrupts: interrupt number to the cpu.
- hpd-gpio: following information about the hotplug gpio pin.
	a) phandle of the gpio controller node.
	b) pin number within the gpio controller.
	c) optional flags and pull up/down.
- clocks: list of clock IDs from SoC clock driver.
	a) hdmi: Gate of HDMI IP bus clock.
	b) sclk_hdmi: Gate of HDMI special clock.
	c) sclk_pixel: Pixel special clock, one of the two possible inputs of
		HDMI clock mux.
	d) sclk_hdmiphy: HDMI PHY clock output, one of two possible inputs of
		HDMI clock mux.
	e) mout_hdmi: It is required by the driver to switch between the 2
		parents i.e. sclk_pixel and sclk_hdmiphy. If hdmiphy is stable
		after configuration, parent is set to sclk_hdmiphy else
		sclk_pixel.
- clock-names: aliases as per driver requirements for above clock IDs:
	"hdmi", "sclk_hdmi", "sclk_pixel", "sclk_hdmiphy" and "mout_hdmi".
- ddc: phandle to the hdmi ddc node
- phy: phandle to the hdmi phy node
- samsung,syscon-phandle: phandle for system controller node for PMU.

Example:

	hdmi {
		compatible = "samsung,exynos4212-hdmi";
		reg = <0x14530000 0x100000>;
		interrupts = <0 95 0>;
		hpd-gpio = <&gpx3 7 1>;
		ddc = <&hdmi_ddc_node>;
		phy = <&hdmi_phy_node>;
		samsung,syscon-phandle = <&pmu_system_controller>;
	};
