net: ethernet: ti: am65-cpsw: Move phy_set_mode_ext() to correct location

In TI's J7200 SoC CPSW5G ports, each of the 4 ports can be configured
as a QSGMII main or QSGMII-SUB port. This configuration is performed
by phy-gmii-sel driver on invoking the phy_set_mode_ext() function.

It is necessary for the QSGMII main port to be configured before any of
the QSGMII-SUB interfaces are brought up. Currently, the QSGMII-SUB
interfaces come up before the QSGMII main port is configured.

Fix this by moving the call to phy_set_mode_ext() from
am65_cpsw_nuss_ndo_slave_open() to am65_cpsw_nuss_init_slave_ports(),
thereby ensuring that the QSGMII main port is configured before any of
the QSGMII-SUB ports are brought up.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>