drm/i915: Enable drm_mm debug when enabling DRM_I915_DEBUG

A frequent issue that arises on shutdown is the drm_mm range manager
complaining of a leak. To aide debugging those, drm can now track the
allocation callsite and print those for the leaks.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161029184214.17329-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Kconfig.debug

@@ -21,6 +21,7 @@ config DRM_I915_DEBUG
         select PREEMPT_COUNT
         select X86_MSR # used by igt/pm_rpm
         select DRM_VGEM # used by igt/prime_vgem (dmabuf interop checks)
+        select DRM_DEBUG_MM
         default n
         help
           Choose this option to turn on extra driver debugging that may affect