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>