clk: meson: meson8b: Export the video clocks

Setting the video clocks requires fine-tuned adjustments of various
video clocks. Export the required ones to allow changing the video clock
for the CVBS and HDMI outputs at runtime.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20210713232510.3057750-7-martin.blumenstingl@googlemail.com