drm/i915: Discard the request queue if we fail to sleep before suspend

If we fail to clear the outstanding request queue before suspending,
mark those requests as lost.

References: https://bugs.freedesktop.org/show_bug.cgi?id=102037


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170826110935.10237-3-chris@chris-wilson.co.uk


Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>