Qualcomm MDSS EDP

MDSS EDP is a edp driver which supports panels that are compatable with
VESA EDP display interface specification.

When configuring the optional properties for external backlight, one should also
configure the gpio that drives the pwm to it.

Required properties
- compatible :				Must be "qcom,mdss-edp".
- reg :						Offset and length of the register set for the
							device.
- reg-names :				Names to refer to register sets related to this
							device
- vdda-supply :				Phandle for vdd regulator device node.
- gpio-panel-en	:			GPIO for supplying power to panel and backlight
							driver.
- gpio-lvl-en	:			GPIO to enable HPD be received by host.
- status :				A string that has to be set to "okay/ok" to enable
						the driver. By default this property will be set to
						"disable". Will be set to "ok/okay" status for
						specific platforms.
- qcom,mdss-fb-map:			pHandle that specifies the framebuffer to which the
					interface is mapped.
- gpio-panel-hpd :			gpio pin use for edp hpd

Optional properties
- qcom,panel-lpg-channel :		LPG channel for backlight.
- qcom,panel-pwm-period :		PWM period in microseconds.


Optional properties:
- qcom,mdss-brightness-max-level:	Specifies the max brightness level supported.
					255 = default value.

Example:
	mdss_edp: qcom,mdss_edp@fd923400 {
		compatible = "qcom,mdss-edp";
		reg = <0xfd923400 0x700>,
			<0xfd8c2000 0x1000>;
		reg-names = "edp_base", "mmss_cc_base";
		vdda-supply = <&pm8941_l12>;
		gpio-panel-en = <&msmgpio 58 0>;
		gpio-lvl-en = <&msmgpio 91 0>;
		qcom,panel-lpg-channel = <7>; /* LPG Channel 8 */
		qcom,panel-pwm-period = <53>;
		status = "disable";
		qcom,mdss-fb-map = <&mdss_fb0>;
		gpio-panel-hpd = <&msmgpio 102 0>;
	};