lavfi: Add OpenCL unsharp mask filter

Intended to replace existing opencl mode of the unsharp filter.
Supports many more pixel formats and works without immediate upload
and download of frame data.  The options are compatible with the
existing filter.

libavfilter/allfilters.c

@@ -339,6 +339,7 @@ static void register_all(void)
     REGISTER_FILTER(TRIM,           trim,           vf);
     REGISTER_FILTER(UNPREMULTIPLY,  unpremultiply,  vf);
     REGISTER_FILTER(UNSHARP,        unsharp,        vf);
+    REGISTER_FILTER(UNSHARP_OPENCL, unsharp_opencl, vf);
     REGISTER_FILTER(USPP,           uspp,           vf);
     REGISTER_FILTER(VAGUEDENOISER,  vaguedenoiser,  vf);
     REGISTER_FILTER(VECTORSCOPE,    vectorscope,    vf);