net: phy: marvell: implement phy_inband_caps() method

Provide an implementation for phy_inband_caps() for Marvell PHYs used
on SFP modules, so that phylink knows the PHYs capabilities.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tIUro-006IUC-Rq@rmk-PC.armlinux.org.uk


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