app/eventdev: simplify signal handling and teardown

app/eventdev: simplify signal handling and teardown

Remove rte_*_dev calls from signal handler callback as signal handlers
are supposed to be light weight.

Split ethdev teardown into Rx and Tx sections, wait for
workers to finish processing after disabling Rx to allow workers
to complete processing currently held packets.

Verified SW event device on ARM64 using the following command:

./build/app/dpdk-test-eventdev -l 7-23 -s 0xf00 --vdev=event_sw0
 -a 0002:02:00.0 -- --prod_type_ethdev --nb_pkts=0 --verbose 2
 --test=pipeline_queue --stlist=o --wlcores 16-23

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