net: phy: micrel: add support for KSZ8895 switch in SMI mode

This patch adds a phy driver for the Micrel KSZ8895 switch.  As the SoC MAC
is directly connected to the switch MAC the link to the switch is always up.

But the KSZ8895 switch can be hardwired in three configuration modes :
- not configurable with eventually an eeprom-stored configuration
- configurable by the mdio/mdc connection (SMI protocol)
- configurable by a SPI connection.

In not configurable mode, the switch starts automatically, but in the
other modes, it must be started programmatically, by writing 1 in
configuration register 1.
We only support the not configurable and mdio/mdc (aka SMI) modes here.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>