dma-buf: allow reserving more than one shared fence slot

Let's support simultaneous submissions to multiple engines.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.kernel.org/patch/10626149/

drivers/gpu/drm/i915/i915_vma.c

@@ -892,7 +892,7 @@ static void export_fence(struct i915_vma *vma,
 	reservation_object_lock(resv, NULL);
 	if (flags & EXEC_OBJECT_WRITE)
 		reservation_object_add_excl_fence(resv, &rq->fence);
-	else if (reservation_object_reserve_shared(resv) == 0)
+	else if (reservation_object_reserve_shared(resv, 1) == 0)
 		reservation_object_add_shared_fence(resv, &rq->fence);
 	reservation_object_unlock(resv);
 }