net: dsa: lan9303: Add port_fast_age and port_fdb_dump methods

Add DSA method port_fast_age as a step to STP support.

Add low level functions for accessing the lan9303 ALR (Address Logic
Resolution).

Added DSA method port_fdb_dump

Signed-off-by: Egil Hjelmeland <privat@egil-hjelmeland.no>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>