app/eventdev: remove unnecessary barriers in perf test

app/eventdev: remove unnecessary barriers in perf test

For "processed_pkts" and "total_latency" functions, no operations should
keep the order that being executed before loading
"worker[i].processed_pkts". Thus rmb is unnecessary before loading.

For "perf_launch_lcores" function, wmb after that the main lcore
updates the variable "t->done", which represents the end of the test
signal, is unnecessary. Because after the main lcore updates this
siginal variable, it will jump out of the launch function loop, and wait
other lcores stop or return error in the main function(evt_main.c).
During this time, there is no important storing operation and thus no
need for wmb.

Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Pavan Nikhilesh <pbhagavatula@marvell.com>