drm/i915/bios: Split parse_driver_features() into two parts

We use the "driver features" block for two different kinds
of data: global data, and per panel data. Split the function
into two parts along that line so that we can start doing the
parsing in two different locations.

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/20220510104242.6099-11-ville.syrjala@linux.intel.com