dt-bindings: display: Turn lvds.yaml into a generic schema

The lvds.yaml file so far was both defining the generic LVDS properties
(such as data-mapping) that could be used for any LVDS sink, but also
the panel-lvds binding.

That last binding was to describe LVDS panels simple enough, and had a
number of other bindings using it as a base to specialise it further.

However, this situation makes it fairly hard to extend and reuse both
the generic parts, and the panel-lvds itself.

Let's remove the panel-lvds parts and leave only the generic LVDS
properties.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220127143045.310199-1-maxime@cerno.tech