dt-bindings: move Atmel ECC508A I2C crypto processor to trivial-devices

Move the binding for the discrete Atmel I2C Elliptic Curve h/w crypto
module to trivial-devices.yaml, as it doesn't belong in atmel-crypto
which describes unrelated on-SoC peripherals.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>