net: mvpp2: use the GoP interrupt for link status changes

This patch adds the GoP link interrupt support for when a port isn't
connected to a PHY. Because of this the phylib callback is never called
and the link status management isn't done. This patch use the GoP link
interrupt in such cases to still have a minimal link management. Without
this patch ports not connected to a PHY cannot work.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Tested-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>