phylink: get rid of separate Cisco SGMII and 802.3z modes

Since the handling of SGMII and 802.3z is now the same, combine the
MLO_AN_xxx constants into a single MLO_AN_INBAND, and use the PHY
interface mode to distinguish between Cisco SGMII and 802.3z.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>