Add some functions to support event in intel gpgpu.

Add some functions to support event in intel gpgpu.

Now runtime prepare command batch first, if can't flush this command
immediately, call cl_gpgpu_event_pending to append the command to event,
when the command batch's wait events completed, than call cl_gpgpu_event_resume
to flush.

Signed-off-by: Yang Rong <rong.r.yang@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>