ethdev: support new VF representor syntax

ethdev: support new VF representor syntax

Current VF representor syntax:
 representor=2          - single representor
 representor=[0-3]      - single range

To prepare for more representor types, this patch adds compatible VF
representor devargs syntax:

vf#:
 representor=vf2          - single representor
 representor=vf[1,3,5]    - single list
 representor=vf[0-3]      - single range
 representor=vf[0,1,4-7]  - list with singles and range

For backwards compatibility, representor "#" is interpreted as "vf#".

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>