drm/i915/bios: Define VBT block 50 (MIPI) contents

Define the contents of VBT block 50 (MIPI).

This was some easly attempt at a MIPI DSI stuff. I'm not sure
this was ever actually used (I certainly don't have any VBTs
with this block), but here's some kind of definition for it
anyway.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503122449.27266-33-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>