eth: mcux: Support devices not using SMI for PHY setup

Some ICs - like DSA switches (e.g. ksz8794) - do not use SMI to setup
and configure PHY.

This change introduces a new Kconfig define - CONFIG_ETH_MCUX_NO_PHY_SMI
- to allow replacing SMI communication with SPI or I2C.

Signed-off-by: Lukasz Majewski <lukma@denx.de>