net: dsa: Centralise global and port setup code into mv88e6xxx.

The port setup code in the individual drivers is identical for 6123,
6171, and 6352, and very similar in 6131. Move it all into mv88e6xxx,
using the chip families to differentiate on features.

Similarly, the global setup is also very similar. Move the majority
into mv8e6xxx.

The chips themselves fall into families. Add helpers which uses the
device IDs to determine if a device is a member of a family or not.
Add some additional device IDs to the existing list, to make these
helper functions more complete. However these IDs are not yet added to
the probe functions.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>