net: bcmgenet: Fix WoL with password after deep sleep

Broadcom STB chips support a deep sleep mode where all register contents
are lost. Because we were stashing the MagicPacket password into some of
these registers a suspend into that deep sleep then a resumption would
not lead to being able to wake-up from MagicPacket with password again.

Fix this by keeping a software copy of the password and program it
during suspend.

Fixes: c51de7f3 ("net: bcmgenet: add Wake-on-LAN support code")
Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>