media: dt-bindings: add bindings document for zx-irdec

It adds the dt-bindings document for ZTE ZX IRDEC remote control
block.

Signed-off-by: Shawn Guo <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Sean Young <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/devicetree/bindings/media/zx-irdec.txt

···
+IR Decoder (IRDEC) on ZTE ZX family SoCs
+
+Required properties:
+ - compatible: Should be "zte,zx296718-irdec".
+ - reg: Physical base address and length of IRDEC registers.
+ - interrupts: Interrupt number of IRDEC.
+
+Exmaples:
+
+	irdec: ir-decoder@111000 {
+		compatible = "zte,zx296718-irdec";
+		reg = <0x111000 0x1000>;
+		interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
+	};