examples/eventdev_pipeline_sw_pmd: add sample app

examples/eventdev_pipeline_sw_pmd: add sample app

This commit adds a sample app for the eventdev library.
The app has been tested with DPDK 17.05-rc2, hence this
release (or later) is recommended.

The sample app showcases a pipeline processing use-case,
with event scheduling and processing defined per stage.
The application receives traffic as normal, with each
packet traversing the pipeline. Once the packet has
been processed by each of the pipeline stages, it is
transmitted again.

The app provides a framework to utilize cores for a single
role or multiple roles. Examples of roles are the RX core,
TX core, Scheduling core (in the case of the event/sw PMD),
and worker cores.

Various flags are available to configure numbers of stages,
cycles of work at each stage, type of scheduling, number of
worker cores, queue depths etc. For a full explaination,
please refer to the documentation.

Signed-off-by: Gage Eads <gage.eads@intel.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>