dt-bindings: clk: axg-clkc: add Video Clocks

Add clock IDs for the video clocks.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200915124553.8056-2-narmstrong@baylibre.com