net: dsa: mv88e6xxx: rename chip header

The mv88e6xxx.h is meant to contains the chip structures and data.
Rename it to chip.h, as for other source/header pairs of the driver.

At the same time, ensure that relative header inclusions are separated
by a newline and sorted alphabetically.

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