net: dsa: microchip: split ksz_connect_tag_protocol()

All the KSZ switches use the same ksz_connect_tag_protocol while they
don't support all the KSZ tag protocols. So if, for some reason, a given
switch tries to connect another KSZ tag protocol, it won't fail.

Split the common ksz_connect_tag_protocol() into switch-specific
operations. This way, each switch will only accept to connect the tag
protocol it supports.
Remove the no longer used common operation.

Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20260505-clean-ksz-driver-v1-9-05d70fa42461@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>