drivers: ethernet: nxp_enet: Handle -ENOTSUP for fixed-link in PHY config

Modified nxp_enet_phy_configure to handle -ENOTSUP returned by the PHY
driver, indicating a fixed-link setup. If -ENOTSUP is returned, a warning
is logged, and PHY configuration is skipped without causing initialization
to fail.

Signed-off-by: Ofir Shemesh <ofirshemesh777@gmail.com>