drm/ttm: add io_mem_pfn callback

This allows the driver to handle io_mem mappings on their own.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -1574,6 +1574,7 @@ struct ttm_bo_driver nouveau_bo_driver = {
 	.fault_reserve_notify = &nouveau_ttm_fault_reserve_notify,
 	.io_mem_reserve = &nouveau_ttm_io_mem_reserve,
 	.io_mem_free = &nouveau_ttm_io_mem_free,
+	.io_mem_pfn = ttm_bo_default_io_mem_pfn,
 };
 
 struct nvkm_vma *