drivers: net: xgene: Poll link status via GPIO

When 10GbE SFP+ module is not plugged in or cable is not connected,
the link status register does not report the proper state due
to floating signal. This patch checks the module present status via an
GPIO to determine whether to ignore the link status register and report
link down.

Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Tested-by: Fushen Chen <fchen@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>