lavu/opencl: replace va_ext.h with standard name

Khronos OpenCL header (https://github.com/KhronosGroup/OpenCL-Headers)
uses cl_va_api_media_sharing_intel.h. And Intel's official OpenCL driver
for Intel GPU (https://github.com/intel/compute-runtime) was compiled
against Khronos OpenCL header. So it's better to align with Khronos.
Signed-off-by: Ruiling Song <ruiling.song@intel.com>

configure

@@ -6472,7 +6472,7 @@ fi
 
 if enabled_all opencl vaapi ; then
     enabled opencl_drm_beignet && enable opencl_vaapi_beignet
-    check_type "CL/cl.h CL/va_ext.h" "clCreateFromVA_APIMediaSurfaceINTEL_fn" &&
+    check_type "CL/cl.h CL/cl_va_api_media_sharing_intel.h" "clCreateFromVA_APIMediaSurfaceINTEL_fn" &&
         enable opencl_vaapi_intel_media
 fi
 

libavutil/hwcontext_opencl.c

@@ -50,7 +50,7 @@
 #include <mfx/mfxstructures.h>
 #endif
 #include <va/va.h>
-#include <CL/va_ext.h>
+#include <CL/cl_va_api_media_sharing_intel.h>
 #include "hwcontext_vaapi.h"
 #endif