selftests: hid: allow to compile hid_bpf with LLVM

clang doesn't like to compile a source to the final binary directly:

clang-14: error: cannot specify -o when generating multiple output files

So split the final rule in 2, and ensure we compile all dependencies
before.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>