examples/l2fwd-event: add infra for eventdev

examples/l2fwd-event: add infra for eventdev

Add infra to select event device as a mode to process packets through
command line arguments. Also, allow the user to select the schedule type
to be RTE_SCHED_TYPE_ORDERED, RTE_SCHED_TYPE_ATOMIC or
RTE_SCHED_TYPE_PARALLEL.

Usage:

`--mode="eventdev"` or `--mode="poll"`
`--eventq-sched="ordered"`, `--eventq-sched="atomic"` or
`--event-sched=parallel`

Signed-off-by: Sunil Kumar Kori <skori@marvell.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Acked-by: Nipun Gupta <nipun.gupta@nxp.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>