event/opdl: add PMD main body and helper function

event/opdl: add PMD main body and helper function

This commit adds a OPDL implementation of the eventdev API. The
implementation here is intended to enable the community to use
the OPDL infrastructure under eventdev API.

The main components of the implementation is three files:
  - opdl_evdev.c              Creation, configuration, etc
  - opdl_evdev_xstats.c       helper function to support stats collection
  - opdl_evdev.h              include the main data structure of opdl
                              device and all the function prototype
                              need to be exposed to support eventdev API.

  - opdl_evdev_init.c         implement all initailization helper function

This commit only adds the implementation, no existing DPDK files
are modified.

Signed-off-by: Liang Ma <liang.j.ma@intel.com>
Signed-off-by: Peter Mccarthy <peter.mccarthy@intel.com>