net: phylink: add suspend/resume support

Joakim Zhang reports that Wake-on-Lan with the stmmac ethernet driver broke
when moving the incorrect handling of mac link state out of mac_config().
This reason this breaks is because the stmmac's WoL is handled by the MAC
rather than the PHY, and phylink doesn't cater for that scenario.

This patch adds the necessary phylink code to handle suspend/resume events
according to whether the MAC still needs a valid link or not. This is the
barest minimum for this support.

Reported-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Tested-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>