dt-bindings: net: ti: k3-am654-cpsw-nuss: evaluate fixed-link property

Since the fixed-link (phyless) mode of operation is supported by the
CPSW MAC, include "fixed-link" in the set of properties to be evaluated.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Link: https://patch.msgid.link/20250411060917.633769-3-s-vadapalli@ti.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>