net: keystone_net: register eth PHYs on MDIO bus

net: keystone_net: register eth PHYs on MDIO bus

As MDIO bus has been added we can register PHYs with it.
After registration, the PHY driver will be probed according to the
hardware on board.

Startup PHY at the ethernet open.

Use phy_startup() instead of keystone_get_link_status() when eth open,
as it verifies PHY link inside and SGMII link is checked before.

For K2HK evm PHY configuration at init was absent, so don't enable
phy config at init for k2hk evm.

Acked-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>