net: dsa: b53: Add ability to enable/disable port interrupts

Some switches expose individual interrupt line(s) for port specific
event(s), allow configuring these interrupts at an appropriate time
during port_enable/disable callbacks where all port specific resources
are known to be set-up and ready for use.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>