net: dsa: realtek: rtl8365mb: add support for rtl8_4t

The trailing tag is also supported by this family. The default is still
rtl8_4 but now the switch supports changing the tag to rtl8_4t.

Reintroduce the dropped cpu in struct rtl8365mb (removed by 6147631c).

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>