net: dsa: mv88e6060: add phylink_get_caps implementation

Add a phylink_get_caps implementation for Marvell 88e6060 DSA switch.
This is a fast ethernet switch, with internal PHYs for ports 0 through
4. Port 4 also supports MII, REVMII, REVRMII and SNI. Port 5 supports
MII, REVMII, REVRMII and SNI without an internal PHY.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/E1qUkx7-003dMX-9b@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>