drm/i915: Include intel_engine_is_idle() status in engine pretty-printer

Upon parking, if we discover an active engine we dump its state. Follow
that state with an indication of whether the engine was idle.

References: https://bugs.freedesktop.org/show_bug.cgi?id=103479
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171107152211.19930-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1835,6 +1835,7 @@ void intel_engine_dump(struct intel_engine_cs *engine, struct drm_printer *m)
 	}
 	spin_unlock_irq(&b->rb_lock);
 
+	drm_printf(m, "Idle? %s\n", yesno(intel_engine_is_idle(engine)));
 	drm_printf(m, "\n");
 }