net: mvneta: implement pcs_inband_caps() method

Report the PCS in-band capabilities to phylink for Marvell NETA
interfaces.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tIUs9-006IUb-Au@rmk-PC.armlinux.org.uk


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