mlxsw: reg: Add Switch VID to FID Allocation register definition

An incoming packet can be classified into a filtering identifer (FID)
based on its VID or incoming port and VID ({Port, VID}).

Add the SVFA register, which controls this mapping.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>