drm/i915: Reset context image on engines after triggering the reset

We try to fixup the context image after the reset to ensure that there
are no more pending writes from the hw that may conflict and to fixup
any that were in flight.

Fixes: a1ef70e1 ("drm/i915: Add support for per engine reset recovery")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-2-chris@chris-wilson.co.uk


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>