Device-Tree bindings for hdmi video driver

Required properties:
- compatible: value should be "fsl,imx6q-hdmi-video".
- fsl,hdcp: define the property in dts, hdmi driver will initalize for hdcp,
  otherwise hdcp function will not supported.
- fsl,phy_reg_vlev: hdmi phy register,Voltage Level Control Register offset 0x0e,
  adjust hdmi phy signal voltage level.
- fsl,phy_reg_cksymtx: hdmi phy register, clock symbol and transmitter control
  register offset 0x09, adjust hdmi signal pre-emphasis.

Example:

	hdmi_video {
		compatible = "fsl,imx6q-hdmi-video";
		fsl,hdcp;
		fsl,phy_reg_vlev = <0x0294>;
		fsl,phy_reg_cksymtx = <0x800d>;
	};