drm/i915: Detect a failed GPU reset+recovery

If we can't recover the GPU after the reset, mark it as wedged to cancel
the outstanding tasks and to prevent new users from trying to use the
broken GPU.

v2: Check the same ring is hung again before declaring the reset broken.
v3: use engine_stalled (Mika)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1484668747-9120-6-git-send-email-mika.kuoppala@intel.com