selftests/hid: ensure CKI can compile our new tests on old kernels

In the same way than commit ae7487d1 ("selftests/hid: ensure we can
compile the tests on kernels pre-6.3") we should expose struct hid_bpf_ops
when it's not available in vmlinux.h.

So unexpose an eventual struct hid_bpf_ops, include vmlinux.h, and
re-export struct hid_bpf_ops.

Fixes: d7696738 ("selftests/hid: convert the hid_bpf selftests with struct_ops")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202406270328.bscLN1IF-lkp@intel.com/
Link: https://patch.msgid.link/20240701-fix-cki-v2-1-20564e2e1393@kernel.org


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