net: dsa: mv88e6xxx: add Energy Detect ops

The 88E6352 family supports Energy Detect and has one bit for Sense and
one bit for periodically transmit NLP (Energy Detect+TM). The 88E6390
family adds another bit to distinguish Auto or SW wake-up. Chips
supporting EEE all have an EEE Enabled bit in the Port Status Register.

This patch adds new ops for the PHY Energy Detect accesses.

This also allows us to get rid of the MV88E6XXX_FLAG_EEE flag.

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