libbpf: Add enum64 support for btf_dump

Add enum64 btf dumping support. For long long and unsigned long long
dump, suffixes 'LL' and 'ULL' are added to avoid compilation errors
in some cases.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220607062631.3720526-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>