net: stmmac: Support WOL with phy

Currently, the stmmac driver WOL implementation relies on MAC's PMT
feature. We have a case: the MAC HW doesn't enable PMT, instead, we
rely on the phy to support WOL. Implement the support for this case.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>