drm: document drm_display_info

We seem to have a bit a mess in how to describe the bus formats, with
a multitude of competing ways. Might be best to consolidate it all and
use MEDIA_BUS_FMT_ also for the hdmi color formats and high color
modes.

Also move all the display_info related functions into drm_connector.c
(there's only one) to group it all together. I did decided against
also moving the edid related display info functions, they seem to fit
better in drm_edid.c. Instead sprinkle a few cross references around.
While at that reduce the kerneldoc for static functions, there's not
point in documenting internals with that much detail really.

v2: Fix typo and move misplaced hunk (Sean).

Cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-19-git-send-email-daniel.vetter@ffwll.ch