drm/i915: Add some more VBT version number comments

Document the VBT version dependency of several other fields.

v2: s/165/155/ for custom_vbt_version (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220715202044.11153-3-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>