drm: add flags to drm_syncobj_find_fence

flags can be used by driver to decide whether need to block wait submission.

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
SIgned-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.kernel.org/patch/10641339/