net: dsa: bcm_sf2: Utilize b53_get_tag_protocol()

Utilize the much more capable b53_get_tag_protocol() which takes care of
all Broadcom switches specifics to resolve which port can have Broadcom
tags enabled or not.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>