net: mscc: ocelot: export NUM_TC constant from felix to common switch lib

We should be moving anything that isn't DSA-specific or SoC-specific out
of the felix DSA driver, and into the common mscc_ocelot switch library.

The number of traffic classes is one of the aspects that is common
between all ocelot switches, so it belongs in the library.

This patch also makes seville use 8 TX queues, and therefore enables
prioritization via the QOS_CLASS field in the NPI injection header.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 70d39a6e

)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
[Xulin: Original patch taken from
https://github.com/vladimiroltean/linux/commits/felix-dsa-tag-vlan-stable]
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>