drm/i915/bios: Define VBT block 28 (EFP DTD) contents

Define the contents of VBT block 28 (EFP DTD).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503122449.27266-27-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>