net: fman: convert to .mac_get_caps()

Convert fman to use the .mac_get_caps() method rather than the
.validate() method.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/E1qsPkA-009wid-Kv@rmk-PC.armlinux.org.uk


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