net: dsa: mv88e6xxx: factorize the switch driver

Now that all drivers support the same set of functions and the same
setup code, drop every model-specific DSA switch driver and replace them
with a common mv88e6xxx driver.

This merges the info tables into one, removes the function exports, the
model-specific files, and update the defconfigs.

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