net: phy: marvell10g: table driven mactype decode

Replace the code-based mactype decode with a table driven approach.
This will allow us to fill in the possible_interfaces cleanly.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1r6VHq-00DDLT-In@rmk-PC.armlinux.org.uk


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