dt-bindings: crypto: add ARTPEC crypto

Document the device tree bindings for the ARTPEC crypto accelerator on
ARTPEC-6 and ARTPEC-7 SoCs.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lars Persson <larper@axis.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>