net: dsa: remove obsolete phylink dsa_switch operations

No driver now uses the DSA switch phylink members, so we can now remove
the method pointers, but we need to leave empty shim functions to allow
those drivers that do not provide phylink MAC operations structure to
continue functioning.

Signed-off-by: Russell King (oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com> # sja1105, felix, dsa_loop
Link: https://patch.msgid.link/E1swKNV-0060oN-1b@rmk-PC.armlinux.org.uk


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