event/sw: add queue-to-port stats

event/sw: add queue-to-port stats

This commit adds a new statistic to the SW eventdev PMD.
The statistic shows how many packets were sent from a
queue to a port. This provides information on how traffic
from a specific queue is being load-balanced to worker cores.

Note that these numbers should be compared across all queue
stages - the load-balancing does not try to perfectly share
each queue's traffic, rather it balances the overall traffic
from all queues to the ports.

The statistic is printed from the rte_eventdev_dump() function,
as well as being made available via the xstats API.

Unit tests have been updated to expect more per-queue statistics,
and the correctness of counts and counts after reset is verified.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>