dt-bindings: crypto: Convert axis,artpec6-crypto to DT schema

Convert the Axis Crypto engine binding to DT schema format. It's a
straight forward conversion.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>