net: pcs: xpcs: implement pcs_inband_caps() method

Report the PCS inband capabilities to phylink for XPCS.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tJ8NW-006L5V-I9@rmk-PC.armlinux.org.uk


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