net: dsa: microchip: move tag_protocol to ksz_common

This patch move the dsa hook get_tag_protocol to ksz_common file. And
the tag_protocol is returned based on the dev->chip_id.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>