net: lan966x: remove PHY reset support

The PHY subsystem as well as the MIIM mdio driver (in case of the
integrated PHYs) will take care of the resets. A separate reset driver
isn't needed. There is no in-tree user of this feature. Remove the
support.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>