hwcontext_opencl: DXVA2 to OpenCL mapping

Using cl_khr_dx9_media_sharing.

configure

@@ -2120,6 +2120,7 @@ HAVE_LIST="
     $TYPES_LIST
     makeinfo
     makeinfo_html
+    opencl_dxva2
     opencl_vaapi_beignet
     opencl_vaapi_intel_media
     perl
@@ -6166,6 +6167,11 @@ if enabled_all opencl vaapi ; then
     fi
 fi
 
+if enabled_all opencl dxva2 ; then
+    check_type "CL/cl_dx9_media_sharing.h" cl_dx9_surface_info_khr &&
+        enable opencl_dxva2
+fi
+
 enabled vdpau &&
     check_cpp_condition vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP" ||
     disable vdpau