dt-bindings: display: add support for ZTE VGA device

It adds bindings doc for ZTE VOU VGA output device.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1491490870-6330-4-git-send-email-shawnguo@kernel.org

Documentation/devicetree/bindings/display/zte,vou.txt

@@ -58,6 +58,18 @@ Required properties:
    integer cells.  The first cell is the offset of SYSCTRL register used
    to control TV Encoder DAC power, and the second cell is the bit mask.
 
+* VGA output device
+
+Required properties:
+ - compatible: should be "zte,zx296718-vga"
+ - reg: Physical base address and length of the VGA device IO region
+ - interrupts : VGA interrupt number to CPU
+ - clocks: Phandle with clock-specifier pointing to VGA I2C clock.
+ - clock-names: Must be "i2c_wclk".
+ - zte,vga-power-control: the phandle to SYSCTRL block followed by two
+   integer cells.  The first cell is the offset of SYSCTRL register used
+   to control VGA DAC power, and the second cell is the bit mask.
+
 Example:
 
 vou: vou@1440000 {
@@ -81,6 +93,15 @@ vou: vou@1440000 {
 			      "main_wclk", "aux_wclk";
 	};
 
+	vga: vga@8000 {
+		compatible = "zte,zx296718-vga";
+		reg = <0x8000 0x1000>;
+		interrupts = <GIC_SPI 86 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&topcrm VGA_I2C_WCLK>;
+		clock-names = "i2c_wclk";
+		zte,vga-power-control = <&sysctrl 0x170 0xe0>;
+	};
+
 	hdmi: hdmi@c000 {
 		compatible = "zte,zx296718-hdmi";
 		reg = <0xc000 0x4000>;