dt-bindings: display: dsi-controller: move clock-master property

The clock-master property is used for the controller and not in the panel,
so move it there.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1c3b18ad-350f-e862-de98-a775e11e132c@gmail.com