net: mvpp2: restructure "link status" interrupt handling

The "link status" interrupt is used for more than just link status.
Restructure mvpp2_link_status_isr() so we can add additional handling.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>