dt-bindings: Add Innolux P097PFG panel bindings

The Innolux P097PFG panel is 9.7" panel with 1536X2048
resolution, it reuse P079ZCA panel driver, so improve
p079ZCA dt-binding to support P097PFG.

Changes in v2:
- None
Changes in v3:
- None
Changes in v4:
- None
Changes in v5:
- use separate file for binding
- keep power supplies as required
Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180702102721.3546-4-heiko@sntech.de

Documentation/devicetree/bindings/display/panel/innolux,p097pfg.txt

+Innolux P097PFG 9.7" 1536x2048 TFT LCD panel
+
+Required properties:
+- compatible: should be "innolux,p097pfg"
+- reg: DSI virtual channel of the peripheral
+- avdd-supply: phandle of the regulator that provides positive voltage
+- avee-supply: phandle of the regulator that provides negative voltage
+- enable-gpios: panel enable gpio
+
+Optional properties:
+- backlight: phandle of the backlight device attached to the panel
+
+Example:
+
+	&mipi_dsi {
+		panel {
+			compatible = "innolux,p079zca";
+			reg = <0>;
+			avdd-supply = <...>;
+			avee-supply = <...>;
+			backlight = <&backlight>;
+			enable-gpios = <&gpio1 13 GPIO_ACTIVE_HIGH>;
+		};
+	};