[media] Documentation: DT: add bindings for ST DELTA

This patch adds DT binding documentation for STMicroelectronics
DELTA V4L2 video decoder.
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/devicetree/bindings/media/st,st-delta.txt

+* STMicroelectronics DELTA multi-format video decoder
+
+Required properties:
+- compatible: should be "st,st-delta".
+- clocks: from common clock binding: handle hardware IP needed clocks, the
+  number of clocks may depend on the SoC type.
+  See ../clock/clock-bindings.txt for details.
+- clock-names: names of the clocks listed in clocks property in the same order.
+
+Example:
+	delta0 {
+		compatible = "st,st-delta";
+		clock-names = "delta", "delta-st231", "delta-flash-promip";
+		clocks = <&clk_s_c0_flexgen CLK_VID_DMU>,
+			 <&clk_s_c0_flexgen CLK_ST231_DMU>,
+			 <&clk_s_c0_flexgen CLK_FLASH_PROMIP>;
+	};