drm/i915: add rcs topology to error state

This might be useful information for developers looking at an error
state.

v2: Place topology towards the end of the error state (Chris)

v3: Reuse common printing code (Michal)

v4: Make this a one-liner (Chris)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180306122857.27317-5-lionel.g.landwerlin@intel.com