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/nouveau/nouveau_drm.c

@@ -1102,7 +1102,6 @@ static int __init
 nouveau_drm_init(void)
 {
 	driver_pci = driver_stub;
-	driver_pci.set_busid = drm_pci_set_busid;
 	driver_platform = driver_stub;
 
 	nouveau_display_options();