arm64: dts: rockchip: enable HDMI CEC on rk3328

This patch enables HDMI CEC on RK3328 devices.

(Unusual) source for the cec clock is taken from the vendor kernel.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>