dt-bindings: soc: mediatek: dvfsrc: Document clock

dt-bindings: soc: mediatek: dvfsrc: Document clock

The DVFSRC hardware has a clock on all platforms.

Instead or proliferating the culture of omitting clock descriptions in
the clock controller drivers or marking them critical instead of
declaring these types of relationships, add this one to the binding.

Any device that wishes to use this binding should figure out their
incomplete or incorrect clock situation first before piling more
features on top.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>