dt-bindings: add device tree binding for Arm TrustZone CryptoCell crypto engine

The Arm TrustZone CryptoCell is a hardware security engine. This patch
adds DT bindings for its Rich Execution Environment crypto engine.

A driver supporting this device is already present in the staging tree.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/crypto/arm-cryptocell.txt

+Arm TrustZone CryptoCell cryptographic engine
+
+Required properties:
+- compatible: Should be "arm,cryptocell-712-ree".
+- reg: Base physical address of the engine and length of memory mapped region.
+- interrupts: Interrupt number for the device.
+
+Optional properties:
+- interrupt-parent: The phandle for the interrupt controller that services
+  interrupts for this device.
+- clocks: Reference to the crypto engine clock.
+- dma-coherent: Present if dma operations are coherent.
+
+Examples:
+
+       arm_cc712: crypto@80000000 {
+               compatible = "arm,cryptocell-712-ree";
+               interrupt-parent = <&intc>;
+               interrupts = < 0 30 4 >;
+               reg = < 0x80000000 0x10000 >;
+
+       };