net: phy: marvell-88x2222: check that link is operational

Some SFP modules uses RX_LOS for link indication. In such cases link
will be always up, even without cable connected. RX_LOS changes will
trigger link_up()/link_down() upstream operations. Thus, check that SFP
link is operational before actual read link status.

If there is no SFP cage connected to the tranciever, check only PMD
Recieve Signal Detect register.

Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>