net: phy: used genphy_soft_reset for phy reset in LAN87xx

Replaced the current code of resetting of LAN87xx phy to
genphy_soft_reset library function.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>