selftests: spectrum-2: Extend and move trace helpers

Allow to specify number of trace hits and move helpers
to the beginning of the file.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>