clk: meson: meson8b: Make the video clock trees mutable

Switch from the "_ro" clock op variants to the mutable ones for all
video clocks. This will allow the VPU driver to change the clocks as
needed for the different video output modes.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20210713232510.3057750-6-martin.blumenstingl@googlemail.com