drm/ttm: add drm gem ttm helpers, starting with drm_gem_ttm_print_info()

Now with ttm_buffer_object being a subclass of drm_gem_object we can
easily lookup ttm_buffer_object for a given drm_gem_object, which in
turn allows to create common helper functions.

This patch starts off with a drm_gem_ttm_print_info() helper function
which adds some ttm specific lines to the debug output.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20190904054740.20817-3-kraxel@redhat.com

drivers/gpu/drm/Kconfig

@@ -172,6 +172,13 @@ config DRM_VRAM_HELPER
 	help
 	  Helpers for VRAM memory management
 
+config DRM_TTM_HELPER
+	tristate
+	depends on DRM
+	select DRM_TTM
+	help
+	  Helpers for ttm-based gem objects
+
 config DRM_GEM_CMA_HELPER
 	bool
 	depends on DRM