bpflist: Display processes with running BPF programs and maps

bpflist: Display processes with running BPF programs and maps

This tool displays processes with running BPF programs and maps,
and also optionally kprobes and uprobes. This is a poor-man's version
that snoops BPF file descriptors, as proposed by @brendangregg.

Example:

```
PID    COMM             TYPE     COUNT
4058   fileslower       prog     4
4058   fileslower       map      2
4106   bashreadline     map      1
4106   bashreadline     prog     1
```

Resolves #1036.