arm64: dts: allwinner: a64: Add CEC clock to HDMI

Experimentation determined that HDMI CEC controller inside DW HDMI block
depends on 32k clock from RTC. If this clock is tampered with, HDMI CEC
communication starts or stops working, depending on situation.

SoC user manual doesn't say anything about CEC, so this was overlooked.
Fix this by adding dependency to RTC 32k clock.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20211120073448.32480-2-jernej.skrabec@gmail.com