net: dsa: felix: add definitions for the stream filter counters

TSN stream (802.1Qci, 802.1CB) filters are also accessed through
STAT_VIEW, just like the port registers, but these counters are per
stream, rather than per port. So we don't keep them in
ocelot_port_update_stats().

What we can do, however, is we can create register definitions for them
just like we have for the port counters, and delete the last remaining
user of the SYS_CNT register + a group index (read_gix).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>