eventdev: introduce specialized enqueue forward op variant

Introducing the rte_event_enqueue_new_burst() for enabling the
PMD, an optimization opportunity to optimize if all the events in
the enqueue burst has the op type of RTE_EVENT_OP_FORWARD.

If a PMD does not have any optimization opportunity
for this operation then the PMD can choose the generic enqueue
burst PMD callback as the fallback.

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