net: ethernet: ti: am65-cpsw: VLAN-aware CPSW only if !DSA

net: ethernet: ti: am65-cpsw: VLAN-aware CPSW only if !DSA

Only configure VLAN-aware CPSW mode if no port is used as DSA CPU port.
VLAN-aware mode interferes with some DSA tagging schemes and makes stacking
DSA switches downstream of CPSW impossible. Previous attempts to address
the issue linked below.

Link: https://lore.kernel.org/netdev/20240227082815.2073826-1-s-vadapalli@ti.com/
Link: https://lore.kernel.org/linux-arm-kernel/4699400.vD3TdgH1nR@localhost/
Co-developed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://patch.msgid.link/20250110125737.546184-1-alexander.sverdlin@siemens.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>