net: enetc: use lynx_pcs_create_mdiodev()

commit  ddbe59d31865e057e2c814f725043acc373a5e60 from
https://github.com/nxp-imx/linux-imx lf-6.1.y

Use the newly introduced lynx_pcs_create_mdiodev() which simplifies the
creation and destruction of the lynx PCS.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit b7d5d043

)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>