dt-bindings: Document STM32 CRC bindings

Document device tree bindings for the STM32 CRC (crypto CRC32)
Signed-off-by: NFabien Dessenne <fabien.dessenne@st.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/crypto/st,stm32-crc.txt

+* STMicroelectronics STM32 CRC
+
+Required properties:
+- compatible: Should be "st,stm32f7-crc".
+- reg: The address and length of the peripheral registers space
+- clocks: The input clock of the CRC instance
+
+Optional properties: none
+
+Example:
+
+crc: crc@40023000 {
+	compatible = "st,stm32f7-crc";
+	reg = <0x40023000 0x400>;
+	clocks = <&rcc 0 12>;
+};