dt-bindings: rng: atmel-trng: add new compatible

Add compatible for new IP found on sam9x60 SoC.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>