net: dsa: microchip: enable EEE support

Some of KSZ9477 family switches provides EEE support. To enable it, we
just need to register set_mac_eee/set_mac_eee handlers and validate
supported chip version and port.

Currently supported chip variants are: KSZ8563, KSZ9477, KSZ9563,
KSZ9567, KSZ9893, KSZ9896, KSZ9897. KSZ8563 supports EEE only with
100BaseTX/Full.  Other chips support 100BaseTX/Full and 1000BaseTX/Full.
Low Power Idle configuration is not supported and currently not
documented in the datasheets.

EEE PHY specific tunings are not documented in the switch datasheets, but can
overlap with KSZ9131 specification.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>