drm: Move all decl for drm_edid.c to drm_edid.h

Some were still left in drm_crtc.h. Also include drm_edid.h in the
rst files.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160831160913.12991-4-daniel.vetter@ffwll.ch