drm/i915: Mark all incomplete requests as -EIO when wedged

Similarly to a normal reset, after we mark the GPU as wedged (completely
fubar and no more requests can be executed), set the error status on all
the in flight requests.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170110172246.27297-4-chris@chris-wilson.co.uk