media: bpf: add bpf function to report mouse movement

Some IR remotes have a directional pad or other pointer-like thing that
can be used as a mouse. Make it possible to decode these types of IR
protocols in BPF.

Cc: netdev@vger.kernel.org
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>