net: dsa: mv88e6xxx: expose mv88e6xxx_num_databases

The mv88e6xxx_num_databases will be used by shared code, so move it
inline to the header file.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>