net: phy: Add Wake-on-LAN driver for Microsemi PHYs.

Wake-on-LAN (WoL) is an Ethernet networking standard that allows
a computer/device to be turned on or awakened by a network message.

VSC8531 PHY can support this feature configure by driver set function.
WoL status get by driver get function.

Tested on Beaglebone Black with VSC 8531 PHY.

Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@microsemi.com>
Signed-off-by: David S. Miller <davem@davemloft.net>