dt-bindings: rng: meson: add meson-rng-s4 compatible

Add compatible for hardware number generator node for
Amlogic S4-series.

Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>