drm/i915/bios: Split VBT parsing to global vs. panel specific parts

Parsing the panel specific data (anything that depends on panel_type)
from VBT is currently happening too early. Split the whole thing
into global vs. panel specific parts so that we can start doing
the panel specific parsing at a later time.

v2: Clarify that this is about panel_type (Jani)
    Split out the leak checks (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220510104242.6099-12-ville.syrjala@linux.intel.com