drm: call drm_gem_object_funcs.mmap with fake offset

The fake offset is going to stay, so change the calling convention for
drm_gem_object_funcs.mmap to include the fake offset.  Update all users
accordingly.

Note that this reverts 83b8a6f242 ("drm/gem: Fix mmap fake offset
handling for drm_gem_object_funcs.mmap") and on top then adds the fake
offset to  drm_gem_prime_mmap to make sure all paths leading to
obj->funcs->mmap are consistent.

v3: move fake-offset tweak in drm_gem_prime_mmap() so we have this code
    only once in the function (Rob Herring).

Fixes: 83b8a6f242 ("drm/gem: Fix mmap fake offset handling for drm_gem_object_funcs.mmap")
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20191127092523.5620-2-kraxel@redhat.com

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -514,13 +514,6 @@ EXPORT_SYMBOL(ttm_bo_mmap);
 int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
 {
 	ttm_bo_get(bo);
-
-	/*
-	 * FIXME: &drm_gem_object_funcs.mmap is called with the fake offset
-	 * removed. Add it back here until the rest of TTM works without it.
-	 */
-	vma->vm_pgoff += drm_vma_node_start(&bo->base.vma_node);
-
 	ttm_bo_mmap_vma_setup(bo, vma);
 	return 0;
 }