event/dlb2: add definitions shared with LKM or shared code

event/dlb2: add definitions shared with LKM or shared code

Add headers containing structs and constants shared between
the PMD and the shared code.  The term shared code refers to
the code that implements the hardware interface. The shared code
is introduced in the probe patch, and then is extended as
additional eventdev PMD entry points are added to the patchset.
In the case of the bifurcated PMD (to be introduced in the
future), the shared code is contained in the Linux kernel
module itself.

Signed-off-by: Timothy McDaniel <timothy.mcdaniel@intel.com>
Reviewed-by: Gage Eads <gage.eads@intel.com>