dt-bindings: rng: Add Exynos850 support to exynos-trng

dt-bindings: rng: Add Exynos850 support to exynos-trng

The TRNG block in Exynos850 is pretty much the same as in Exynos5250,
but there are two clocks that has to be controlled to make it work:
  1. Functional (operating) clock: called ACLK in Exynos850, the same as
     "secss" clock in Exynos5250
  2. Interface (bus) clock: called PCLK in Exynos850. It has to be
     enabled in order to access TRNG registers

Document Exynos850 compatible and the related clock changes.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>