net/mlx5: support new flow counter API

net/mlx5: support new flow counter API

This patch updates the functions performing the Verbs ibrary calls
in order to support different versions of the library.
The functions:
  - flow_verbs_counter_new()
  - flow_verbs_counter_release()
  - flow_verbs_counter_query()
now have the several compilation branches, depending on the
counters support found in the system at compile time.

The flow_verbs_counter_create() function is introduced as
helper for flow_verbs_counter_new(), actually this helper
create the counters with Verbs.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>