eventdev: add errno-style return values
This commit adds rte_errno return values to rte_event_enqueue_burst() and
rte_event_dequeue_burst().
These return values allows user software to differentiate between an
invalid argument (such as an invalid queue_id or sched_type in an enqueued
event) and backpressure from the event device.
The port and device ID checks are placed in RTE_LIBRTE_EVENTDEV_DEBUG
header guards to avoid the performance hit in non-debug execution.
Signed-off-by: Gage Eads <gage.eads@intel.com>