Define the contents of VBT block 5 (Generic Mode Table).

Details were mostly gleaned from some VBIOS sources.

There are apparently two variants of the block: ALM only
vs. MGM, defined here as bdb_generic_mode_table_alm
and bdb_generic_mode_table_mgm. And those are the only two
platforms where I've seen this block.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503122449.27266-12-ville.syrjala@linux.intel.comAcked-by: Jani Nikula <jani.nikula@intel.com>