net: dsa: b53: Turn on Broadcom tags

Enable Broadcom tags for b53 devices, except 5325 and 5365 which use a
different Broadcom tag format not yet supported by net/dsa/tag_brcm.c.

We also make sure that we can turn on Broadcom tags on a CPU port number
that is capable of that: 5, 7 or 8.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>