net: dsa: microchip: remove KSZ9477 PHY errata handling

The KSZ9477 PHY errata handling code has now been moved into the Micrel
PHY driver, so it is no longer needed inside the DSA switch driver.
Remove it.

Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>