net: dsa: rename probe and remove switch functions

This commit brings no functional changes. It gets rid of the underscore
prefixed _dsa_register_switch and _dsa_unregister_switch functions in
favor of dsa_switch_probe() which parses and adds a switch to a tree and
dsa_switch_remove() which removes a switch from a tree.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>