drm/i915: Show cursor size in debugfs/i915_display_info

Inlcude the pipe-size and cursor-size in debugfs.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>