net: phy: keep track of the PHY suspend state

In order to avoid double calls to phydev->drv->suspend and resume, keep
track of whether the PHY has already been suspended as a consequence of
a successful call to phy_suspend(). We will use this in our MDIO bus
suspend/resume hooks to avoid a double suspend call.

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