ipq40xx: net: phy: ar40xx: remove PHY handling

ipq40xx: net: phy: ar40xx: remove PHY handling

Since we now have proper PHY driver for the QCA807x PHY-s, lets remove
PHY handling from AR40xx.

This removes PHY driver, PHY GPIO driver and PHY init code.
AR40xx still needs to handle PSGMII calibration as that requires R/W
from the switch, so I am unable to move it into PHY driver.

This also converted the AR40xx driver to use OF_MDIO to find the MDIO
bus as it now cant be set through the PHY driver.
So lets depend on OF_MDIO in KConfig.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>