eventdev: quiesce an event port

eventdev: quiesce an event port

Add function to quiesce any core specific resources consumed by
the event port.

When the application decides to migrate the event port to another lcore
or teardown the current lcore it may to call `rte_event_port_quiesce`
to make sure that all the data associated with the event port are released
from the lcore, this might also include any prefetched events.

While releasing the event port from the lcore, this function calls the
user-provided flush callback once per event.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>