selftests/bpf: Add __int128-specific tests for typed data dump

Add tests for __int128 display for platforms that support it.
__int128s are dumped as hex values.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626770993-11073-3-git-send-email-alan.maguire@oracle.com