net: dsa: mxl-gsw1xx: fix .shutdown driver operation

net: dsa: mxl-gsw1xx: fix .shutdown driver operation

The .shutdown operation should call dsa_switch_shutdown() just like
it is done also by the sibling lantiq_gswip driver. Not doing that
results in shutdown or reboot hanging and waiting for the CPU port
becoming free, which introduces a longer delay and a WARNING before
shutdown or reboot in case the driver is built-into the kernel.
Fix this by calling dsa_switch_shutdown() in the driver's shutdown
operation, harmonizing it with what is done in the lantiq_gswip
driver. As a side-effect this now allows to remove the previously
exported gswip_disable_switch() function which no longer got any
users.

Fixes: 22335939ec907 ("net: dsa: add driver for MaxLinear GSW1xx switch family")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/77ed91a5206e5dbf5d3e83d7e364ebfda90d31fd.1765241054.git.daniel@makrotopia.org
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>