arm64: dts: meson: add missing g12 rng clock

This adds the missing perpheral clock for the RNG for Amlogic G12. As
stated in amlogic,meson-rng.yaml, this isn't always necessary for the
RNG to function, but is better to have in case the clock is disabled for
some reason prior to loading.

Signed-off-by: Scott K Logan <logans@cottsay.net>
Suggested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/520a1a8ec7a958b3d918d89563ec7e93a4100a45.camel@cottsay.net