dt-bindings: rng: rockchip,rk3588-rng: add rk3576-rng compatible

The RK3576 SoC contains another standalone TRNG implementation. While
the register map and hardware is different, it has the same
clocks/interrupts/resets as the RK3588's TRNG, so can go in the same
binding.

Add the compatible and generalise the title/description of the binding
some more.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>