format_args: display fd path
format_args: display fd path

E.g. for calls like this:
```
 ► 0x555555554a57 <main+296>    call   ioctl@plt <ioctl@plt>
        fd: 0x3
        request: 0xae01
        vararg: 0x0
```

We want to display the `fd` as: `fd: 0x3 (/some/path)` fetched from
`readlink -f /proc/$PID/fd/$FD`.

pwndbg/pwndbg,pwndbg/pwndbg,pwndbg/pwndbg,pwndbg/pwndbg