drm: Remove drm_driver->set_busid hook

The only special-case is pci devices, and we can easily handle this in
the core. Do so and drop a pile of boilerplate from drivers.

Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170524145212.27837-5-daniel.vetter@ffwll.ch

drivers/gpu/drm/ast/ast_drv.c

@@ -197,7 +197,6 @@ static struct drm_driver driver = {
 
 	.load = ast_driver_load,
 	.unload = ast_driver_unload,
-	.set_busid = drm_pci_set_busid,
 
 	.fops = &ast_fops,
 	.name = DRIVER_NAME,