net: pcs: mtk-lynxi: fill in PCS supported_interfaces

Fill in the new PCS supported_interfaces member with the interfaces
that the Mediatek LynxI supports.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Acked-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1tTffV-007RoP-8D@rmk-PC.armlinux.org.uk


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