net: fec: add pm runtime force suspend and resume support

Force mii bus into runtime pm suspend state during device suspends,
since phydev state is already PHY_HALTED, and there is no need to
access mii bus during device suspend state. Then force mii bus into
runtime pm resume state when device resumes.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>