net: dsa: mv88e6xxx: add support for mv88e6393x family

The Marvell 88E6393X device is a single-chip integration of a 11-port
Ethernet switch with eight integrated Gigabit Ethernet (GbE)
transceivers and three 10-Gigabit interfaces.

This patch adds functionalities specific to mv88e6393x family (88E6393X,
88E6193X and 88E6191X).

The main differences between previous devices and this one are:
- port 0 can be a SERDES port
- all SERDESes are one-lane, eg. no XAUI nor RXAUI
- on the other hand the SERDESes can do USXGMII, 10GBASER and 5GBASER
  (on 6191X only one SERDES is capable of more than 1g; USXGMII is not
  yet supported with this change)
- Port Policy CTL register is changed to Port Policy MGMT CTL register,
  via which several more registers can be accessed indirectly
- egress monitor port is configured differently
- ingress monitor/CPU/mirror ports are configured differently and can be
  configured per port (ie. each port can have different ingress monitor
  port, for example)
- port speed AltBit w...