ethdev: support PF index in representor

ethdev: support PF index in representor

With Kernel bonding, multiple underlying PFs are bonded, VFs come
from different PF, need to identify representor of VFs unambiguously by
adding PF index.

This patch introduces optional 'pf' section to representor devargs
syntax, examples:
 representor=pf0vf0             - single VF representor
 representor=pf[0-1]sf[0-1023]  - SF representors from 2 PFs

PF type representor is supported by using standalone 'pf' section:
 representor=pf1                - PF representor

Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>