selftests/bpf: Add pruning test case for bpf_spin_lock

selftests/bpf: Add pruning test case for bpf_spin_lock

Test that when reg->id is not same for the same register of type
PTR_TO_MAP_VALUE between current and old explored state, we currently
return false from regsafe and continue exploring.

Without the fix in prior commit, the test case fails.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20221209135733.28851-7-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>