net: dsa: allow switch drivers to implement suspend/resume hooks

Add an abstraction layer to suspend/resume switch devices, doing the
following split:

- suspend/resume the slave network devices and their corresponding PHY
  devices
- suspend/resume the switch hardware using switch driver callbacks

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/net/dsa.h
Simple merge

diff --cc net/dsa/dsa.c
Simple merge

diff --cc net/dsa/dsa_priv.h
Simple merge

diff --cc net/dsa/slave.c
Simple merge