drm/i915: Suppress empty lines from debugfs/i915_gem_objects

This is just so that I don't have to read about the batch pool on
systems that are not using it! Rather than using a newline between the
kernel clients and userspace clients, just distinguish the internal
allocations with a '[k]'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>