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

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>