drm: Track drm_mm allocators and show leaks on shutdown

We can use the kernel's stack tracer and depot to record the allocation
site of every drm_mm user. Then on shutdown, as well as warning that
allocated nodes still reside with the drm_mm range manager, we can
display who allocated them to aide tracking down the leak.

v2: Move Kconfig around so it lies underneath the DRM options submenu.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161031090806.20073-1-chris@chris-wilson.co.uk