drm/i915/bios: Define VBT block 253 (PRD Table) contents

Define the contents of VBT block 253 (PRD Table).

Unfortunately the block has two definitions, with the cutoff
supposedly happening on ICL vs. TGL. Also according to some
notes it might be that the VBIOS (if that's still a thing)
still uses the old definition even on TGL+. Quite the mess.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503122449.27266-36-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>