drm/radeon: deprecate and remove KFD interface

To quote Felix: "For testing KV with current user mode stack, please use
amdgpu. I don't expect this to work with radeon and I'm not planning to
spend any effort on making radeon work with a current user mode stack."

Only compile tested, but should be straight forward.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>