net: DSA: Marvell mv88e6171 switch driver

This is the Marvell driver with some cleanups by Claudio Leite
and myself.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Cc: Claudio Leite <leitec@staticky.com>
Signed-off-by: Claudio Leite <leitec@staticky.com>
Signed-off-by: David S. Miller <davem@davemloft.net>