drivers: eth: mcux: Fix PHY access in eth_mcux_phy_setup

It is necessary to poll the ENET_EIR_MII bit before reading
the data register as explained in the i.MX RT1060 reference
manual in chapter 41.7.17.4.
Use PHY_* functions from NXP HAL to correctly access the PHY
registers.

Signed-off-by: Armand Ciejak <armandciejak@users.noreply.github.com>