net/enic: add minimal VF representor

net/enic: add minimal VF representor

Enable the minimal VF representor without Tx/Rx and flow API support.

1. Enable the standard devarg 'representor'
When the devarg is specified, create VF representor ports.

2. Initialize flowman early during PF probe
Representors require the flowman API from the firmware. Initialize it
before creating VF representors, so probe can detect the flowman
support and fail if not available.

3. Add enic_fm_allocate_switch_domain() to allocate switch domain ID
PFs and VFs on the same VIC adapter can forward packets to each other,
so the switch domain is the physical adapter.

4. Create a vnic_dev lock to serialize concurrent devcmd calls
PF and VF representor ports may invoke devcmd (e.g. dump stats)
simultaneously. As they all share a single PF devcmd instance in the
firmware, use a lock to serialize devcmd calls.

Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>