drm/i915/opregion: Fix CONFIG_ACPI=n builds adding missing intel_opregion_cleanup() prototype

Add the missing intel_opregion_cleanup() prototype fixing CONFIG_ACPI=n
builds.

Fixes: 3e226e4a ("drm/i915/opregion: Cleanup opregion after errors during driver loading")
Cc: Jani Nikula <jani.nikula@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303141610.6L1VO7Gw-lkp@intel.com/


Signed-off-by: Imre Deak <imre.deak@intel.com>