drm/i915/bios: Refactor panel_type code

Make the panel type code a bit more abstract along the
lines of the source of the panel type. For the moment
we have three classes: OpRegion, VBT, fallback.
Well introduce another one shortly.

We can now also print out all the different panel types,
and indicate which one we ultimately selected. Could help
with debugging.

v2: Add .get_panel_type() vfunc (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/20220504150440.13748-8-ville.syrjala@linux.intel.com