net: macb: convert to phylink_generic_validate()

Populate the supported interfaces bitmap and MAC capabilities mask for
the macb driver and remove the old validate implementation.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1mpuRv-00D4rb-Lz@rmk-PC.armlinux.org.uk


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