net: bcmgenet: add Wake-on-LAN support code

Add all the required code to program the GENET hardware to enter
Wake-on-LAN mode and wake using MagicPackets with or without SecureOn
password.

This code is hooked to the build system, but is not yet referenced from
ethtool or the main bcmgenet driver.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>