tools/bpf: add bpffs pretty print btf test for hash/lru_hash maps

Pretty print tests for hash/lru_hash maps are added in test_btf.c.
The btf type blob is the same as pretty print array map test.
The test result:
  $ mount -t bpf bpf /sys/fs/bpf
  $ ./test_btf -p
    BTF pretty print array......OK
    BTF pretty print hash......OK
    BTF pretty print lru hash......OK
    PASS:3 SKIP:0 FAIL:0

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>