cl_khr_mipmap_image: missing testing for clEnqueueFillImage

[bashbaug]

Found while investigating https://github.com/KhronosGroup/OpenCL-Docs/issues/1241.

We do not seem to be testing clEnqueueFillImage on image with mipmaps. According to the spec this should be supported:

https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#image-mipmap-access

When the cl_khr_mipmap_image extension is supported, the clEnqueueReadImage, clEnqueueWriteImage, clEnqueueMapImage, clEnqueueCopyImage, clEnqueueCopyImageToBuffer, clEnqueueCopyBufferToImage, and clEnqueueFillImage functions described above can operate on mipmapped images.