Add clEnqueueMapBuffer and clEnqueueMapImage non-blocking map support.

Add clEnqueueMapBuffer and clEnqueueMapImage non-blocking map support.

There is a unsync map function drm_intel_gem_bo_map_unsynchronized in drm, that can
be used to do non-blocking map. But this function only map gtt, so force to use map
gtt for all clEnqueueMapBuffer and clEnqueueMapImage.

V2: refined comment, and using map_gtt_unsync in clEnqueueMapBuffer/Image
    instead of map_auto to avoid confuse.

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