drm/i915: Free memdup-ed DSI VBT data structures on driver_unload

Make intel_bios_cleanup function free the DSI VBT data structures which
are memdup-ed by parse_mipi_config() and parse_mipi_sequence().

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214082151.25015-2-hdegoede@redhat.com