drm/edid: prefer forward declarations over includes in drm_edid.h

There's no need to include either linux/hdmi.h or drm/drm_mode.h. They
can be removed by using forward declarations.

While at it, group the forward declarations together, and remove the
unnecessary ones.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240104211028.1129606-1-jani.nikula@intel.com