drm/i915: Move debugfs/i915_semaphore_status to i915_engine_info

As the semaphores is just part of the engine, include it with the
general pretty printer universally used for debugging.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171120205504.21892-4-chris@chris-wilson.co.uk