drm/edid: move edid load declarations to internal header

The EDID loader is internal to drm, not for drivers.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d58a59fede286caa8766e0813f4be492a7200287.1666614699.git.jani.nikula@intel.com