net: ethernet: ti: am65-cpsw: use cppi5_desc_is_tdcm()

Use cppi5_desc_is_tdcm() helper for teardown indicator detection instead of
hard-coded value.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>