app/crypto-perf: add new PMD benchmarking mode

app/crypto-perf: add new PMD benchmarking mode

This patch adds a new benchmarking mode, which is intended for
microbenchmarking individual parts of the cryptodev framework,
specifically crypto ops alloc-build-free, cryptodev PMD enqueue
and cryptodev PMD dequeue.

It works by first benchmarking crypto operation alloc-build-free
loop (no enqueues/dequeues happening), and then benchmarking
enqueue and dequeue separately, by first completely filling up the
TX queue, and then completely draining the RX queue.

Results are shown as cycle counts per alloc/build/free, PMD enqueue
and PMD dequeue.

One new test mode is added: "pmd-cyclecount"
  (called with --ptest=pmd-cyclecount)

New command-line argument is also added:
  --pmd-cyclecount-delay-ms: this is a pmd-cyclecount-specific parameter
      that controls the delay between enqueue and dequeue. This is
      useful for benchmarking hardware acceleration, as hardware may
      not be able to keep up with enqueued packets. This parameter
      can be increased if there are large amounts of dequeue
      retries.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>