drm/i915: Build DRM range manager selftests for CI

Build the struct drm_mm selftests so that we can trivially run them
within our CI.

"Enable debug, become developer." - Joonas Lahtinen
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170125101102.9010-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Kconfig.debug

@@ -24,6 +24,7 @@ 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 DRM_DEBUG_MM_SELFTEST
 	select DRM_I915_SW_FENCE_DEBUG_OBJECTS
         default n
         help