drm/i915: Disable RPM wakeref assertions during driver shutdown

As with the regular suspend paths, also disable the wakeref assertions
as we disable the driver during shutdown.

Reported-by: Hans de Goede <hdegoede@redhat.com>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2899
Fixes: fe0f1e3b

 ("drm/i915: Shut down displays gracefully on reboot")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210104203905.19248-1-chris@chris-wilson.co.uk