iidc: Introduce iidc.h

Introduce a shared header file used by the 'ice' Intel networking driver
providing RDMA support and the 'irdma' driver to provide a private
interface.

Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>