net: stmmac: notify the PM core of a wakeup event.

In PM_SUSPEND_FREEZE and WOL(Wakeup On Lan) case, when the driver gets a
wakeup event, either the driver or platform specific PM code should notify
the pm core about it, so that the system can wakeup from low power.

In cases where there is no involvement of platform specific PM, it
becomes driver responsibility to notify the PM core to wakeup the
system.

Without this WOL with PM_SUSPEND_FREEZE does not work on STi based SOCs.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>