dt-bindings: consolidate display related bindings

This is a quite large renaming to consolidate display related bindings
into a single "display" directory from various scattered locations of
video, drm, gpu, fb, mipi, and panel. The prior location was somewhat
based on the Linux driver location, but bindings should be independent
of that.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>