dt-bindings: rng: add binding for Rockchip RK3588 RNG

The Rockchip RK3588 SoC has two hardware RNGs accessible to the
non-secure world: an RNG in the Crypto IP, and a standalone RNG that is
new to this SoC.

Add a binding for this new standalone RNG. It is distinct hardware from
the existing rockchip,rk3568-rng, and therefore gets its own binding as
the two hardware IPs are unrelated other than both being made by the
same vendor.

The RNG is capable of firing an interrupt when entropy is ready.

The reset is optional, as the hardware does a power-on reset, and
functions without the software manually resetting it.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>