drm/i915: Include instdone[1] in hangcheck

References:

  Bug 26691 - Spurious hangcheck whilst executing a long shader over a
              large vertex buffer
  https://bugs.freedesktop.org/show_bug.cgi?id=26691



Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>