net: ethernet: ti: am65-cpsw: move free desc queue mode selection in pdata

In preparation of adding more multi-port K3 CPSW versions move free
descriptor queue mode selection in am65_cpsw_pdata, so it can be selected
basing on DT compatibility property.

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>