drm/i915: Add suspend count to error state

For example if we get bug reports with similar error states and
suspend count is always 1, that might lead the Sherlocks to
right general direction.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>