net: stmmac: move xgmac specific phylink caps to dwxgmac2 core

Move the xgmac specific phylink capabilities to the dwxgmac2 support
core.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1qZAXd-005pUP-JL@rmk-PC.armlinux.org.uk


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