pmcstat: implement showing offsets into symbols in top mode

The -I option (and hotkey) is reused for this. Skipping symbol resolution is
moved to the new -A option (and hotkey).

While arguably this violates POLA I think it's a change for the better.
ALso note the -I option was added in head.

Differential Revision: https://reviews.freebsd.org/D21658