drm: move edid property update and add modes out of edid firmware loader

Make the firmware loader more generic and generally useful.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487344854-18777-2-git-send-email-jani.nikula@intel.com