examples/eventdev: check CPU core enabling

examples/eventdev: check CPU core enabling

In the case that the cores are isolated, if "-l" or "-c" parameter is not
added, the cores will not be enabled and can not launch worker function
correctly. In the meanwhile, no error information is reported.

For example:
totally CPUs:16
isolated CPUs:1-8
command: sudo gdb -args ./dpdk-eventdev_pipeline --vdev event_sw0 \
        -- -r1 -t1 -e4 -w F00 -s4 -n0 -c32 -W1000 -D

cores information:
rte_config->lcore_role = {ROLE_RTE, ROLE_OFF, ROLE_OFF, ROLE_OFF,
                          ROLE_OFF, ROLE_OFF, ROLE_OFF, ROLE_OFF,
                          ROLE_OFF, ROLE_RTE, ROLE_RTE, ROLE_RTE,
                          ROLE_RTE, ROLE_RTE, ROLE_RTE, ROLE_RTE}

output information:
...
[main()] lcore 9 executing worker, using eventdev port 0
[main()] lcore 10 executing worker, using eventdev port 1
[main()] lcore 11 executing worker, using eventdev port 2

This is because "RTE_LCORE_FOREACH_WORKER" chooses the enabled core. In
the case that the cores are isolated, "the lcore_role" flag of isolated
cores are set as "ROLE_OFF" by default(not enabled). So if we choose
these isolated cores as workers, "RTE_LCORE_FOREACH_WORKER" will ignore
these cores and not launch worker functions on them.

To fix this, add "-l" parameters to doc and add lcore enabled check.

Fixes: 1094ca96689c ("doc: add SW eventdev pipeline to sample app guide")
Cc: stable@dpdk.org
Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>