net/mlx5: support sub-function representor

net/mlx5: support sub-function representor

This patch adds support for SF representor. Similar to VF representor,
switch port name of SF representor in phys_port_name sysfs key is
"pf<x>sf<y>".

Device representor argument is "representors=sf[list]", list member
could be mix of instance and range. Example:
  representors=sf[0,2,4,8-12,-1]

To probe VF representor and SF representor, need to separate into 2
devices:
  -a <BDF>,representor=vf[list] -a <BDF>,representor=sf[list]

Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>