event/sw: add worker core functions

event/sw: add worker core functions

add the event enqueue, dequeue and release functions to the eventdev.
These also include tracking of stats for observability in the load of
the scheduler.
Internally in the enqueue function, the various types of enqueue
operations, to forward an existing event, to send a new event, to
drop a previous event, are converted to a series of flags which will
be used by the scheduler code to perform the needed actions for that
event.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Gage Eads <gage.eads@intel.com>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>