tools: fix pmdinfo for FreeBSD

tools: fix pmdinfo for FreeBSD

There were a couple of issues which prevented pmdinfo.py from running on
FreeBSD, both of which are fixed by this patch.

* The path to python is not /usr/bin/python as on Linux, so use
  /usr/bin/env to find it on both OS's.
* The path to the pci ids DB is in a different location on FreeBSD,
  so use the platform python library to look in different default
  locations depending on the underlying OS. [There are two possible
  locations to look on FreeBSD, as defined by pciconf manpage, so
  check in both in order of better to worse]

Fixes: c67c9a5c646a ("tools: query binaries for HW and other support information")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>