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

include/drm/drm_gem_ttm_helper.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef DRM_GEM_TTM_HELPER_H
+#define DRM_GEM_TTM_HELPER_H
+
+#include <linux/kernel.h>
+
+#include <drm/drm_gem.h>
+#include <drm/drm_device.h>
+#include <drm/ttm/ttm_bo_api.h>
+#include <drm/ttm/ttm_bo_driver.h>
+
+#define drm_gem_ttm_of_gem(gem_obj) \
+	container_of(gem_obj, struct ttm_buffer_object, base)
+
+void drm_gem_ttm_print_info(struct drm_printer *p, unsigned int indent,
+			    const struct drm_gem_object *gem);
+
+#endif