selftests/bpf: make use of PROCMAP_QUERY ioctl if available

selftests/bpf: make use of PROCMAP_QUERY ioctl if available

Instead of parsing text-based /proc/<pid>/maps file, try to use
PROCMAP_QUERY ioctl() to simplify and speed up data fetching.
This logic is used to do uprobe file offset calculation, so any bugs in
this logic would manifest as failing uprobe BPF selftests.

This also serves as a simple demonstration of one of the intended uses.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20240806230319.869734-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>