dt/bindings: Add bindings for the PIC32 random number generator

Document the devicetree bindings for the random number generator found
on Microchip PIC32 class devices.
Signed-off-by: NJoshua Henderson <joshua.henderson@microchip.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/microchip,pic32-rng.txt

+* Microchip PIC32 Random Number Generator
+
+The PIC32 RNG provides a pseudo random number generator which can be seeded by
+another true random number generator.
+
+Required properties:
+- compatible : should be "microchip,pic32mzda-rng"
+- reg : Specifies base physical address and size of the registers.
+- clocks: clock phandle.
+
+Example:
+
+	rng: rng@1f8e6000 {
+		compatible = "microchip,pic32mzda-rng";
+		reg = <0x1f8e6000 0x1000>;
+		clocks = <&PBCLK5>;
+	};