drm/i915: Select STACKDEPOT for DRM_I915_DEBUG

select in Kconfig isn't recursive, we need to select the stuff our
selects select, too. Fix that.
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180320125009.2305-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/Kconfig.debug

@@ -25,6 +25,7 @@ config DRM_I915_DEBUG
         select X86_MSR # used by igt/pm_rpm
         select DRM_VGEM # used by igt/prime_vgem (dmabuf interop checks)
         select DRM_DEBUG_MM if DRM=y
+        select STACKDEPOT if DRM=y # for DRM_DEBUG_MM
 	select DRM_DEBUG_MM_SELFTEST
 	select SW_SYNC # signaling validation framework (igt/syncobj*)
 	select DRM_I915_SW_FENCE_DEBUG_OBJECTS