drm/i915: Record BB_ADDR for every ring

Every ring seems to have a BB_ADDR registers, so include them all in the
error state.

v2: Also include the _UDW on BDW

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>