hwrng: st - Provide DT bindings for ST's Random Number Generator

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/st,rng.txt

+STMicroelectronics HW Random Number Generator
+----------------------------------------------
+
+Required parameters:
+compatible	: Should be "st,rng"
+reg		: Base address and size of IP's register map.
+clocks		: Phandle to device's clock (See: ../clocks/clock-bindings.txt)
+
+Example:
+
+rng@0xfee80000 {
+	compatible      = "st,rng";
+	reg		= <0xfee80000 0x1000>;
+	clocks          = <&clk_sysin>;
+}