drm/i915/execlists: Notify context-out for lost requests

drm/i915/execlists: Notify context-out for lost requests

When cancelling requests, also send the notification to any listeners
(gvt) that the request is no longer scheduled on hw. They may require to
keep the in/out exactly balanced, and so the reuse after the reset may
confuse the listener.

Fixes: f0191c3164ea ("drm/i915/execlists: Unwind incomplete requests on resets")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Zhenyu Wang" <zhenyuw@linux.intel.com>
Cc: "Wang, Zhi A" <zhi.a.wang@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170926101720.9479-1-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>