selftests/hid: convert the hid_bpf selftests with struct_ops

We drop the need for the attach() bpf syscall, but we need to set up
the hid_id field before calling __load().

The .bpf.c part is mechanical: we create one struct_ops per HID-BPF
program, as all the tests are for one program at a time.

Link: https://lore.kernel.org/r/20240608-hid_bpf_struct_ops-v3-4-6ac6ade58329@kernel.org


Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>