drm/ast: Convert AST driver to |struct drm_gem_vram_object|

The data structure |struct drm_gem_vram_object| and its helpers replace
|struct ast_bo|. It's the same implementation; except for the type names.

v4:
	* cleanups from checkpatch.pl

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20190508082630.15116-10-tzimmermann@suse.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/ast/Kconfig

@@ -3,7 +3,7 @@ config DRM_AST
 	depends on DRM && PCI && MMU
 	select DRM_TTM
 	select DRM_KMS_HELPER
-	select DRM_TTM
+	select DRM_VRAM_HELPER
 	help
 	 Say yes for experimental AST GPU driver. Do not enable
 	 this driver without having a working -modesetting,