dt-bindings: phy: Document the Synopsys MIPI DPHY Rx bindings

Add device-tree bindings documentation for SNPS DesignWare MIPI D-PHY in
RX mode.

Signed-off-by: Luis Oliveira <luis.oliveira@synopsys.com>

Author: Luis Oliveira

Documentation/devicetree/bindings/phy/snps,dw-dphy-rx.txt

@@ -0,0 +1,29 @@
+Synopsys DesignWare MIPI Rx D-PHY block details
+
+Description
+-----------
+
+The Synopsys MIPI D-PHY controller supports MIPI-DPHY in receiver mode.
+Please refer to phy-bindings.txt for more information.
+
+Required properties:
+- compatible		: Shall be "snps,dw-dphy-rx".
+- #phy-cells		: Must be 1.
+- bus-width		: Size of the test interface data bus (8 bits->8 or
+			  12bits->12).
+- snps,dphy-frequency	: Frequency at which D-PHY should start, configurable.
+			  Check Synopsys databook. (-kHz)
+- reg			: Test interface register. This correspondes to the
+			  physical base address of the controller and size of
+			  the device memory mapped registers; Check Synopsys
+			  databook.
+
+Example:
+
+	mipi_dphy_rx1: dphy@d00003040 {
+		compatible = "snps,dw-dphy-rx";
+		#phy-cells = <1>;
+		bus-width = <12>;
+		snps,dphy-frequency = <300000>;
+		reg = <0xd0003040 0x20>;
+	};