dsa: Register the none tagger ops

The none tagger is special in that it does not live in a tag_*.c file,
but is within the core. Register/unregister when DSA is
loaded/unloaded.

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