selftests/bpf: add test case for bpf_map_lookup_percpu_elem

test_progs:
Tests new ebpf helpers bpf_map_lookup_percpu_elem.

Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
Link: https://lore.kernel.org/r/20220511093854.411-3-zhoufeng.zf@bytedance.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>