dt-bindings: crypto: Convert ti,omap4-des to DT schema

Convert the TI OMAP DES binding to DT schema format.

Drop "ti,hwmods" as it is not actually used for this binding. Only
OMAP2 platforms are using it.

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>