dt-bindings: rng: add BCM2711 RNG compatible

The BCM2711 has a RNG200 block, so document its compatible string.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Stephen Brennan <stephen@brennan.io>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>