mlxsw: spectrum_trap: Prepare policers for registration with devlink

Prepare an array of policer IDs to register with devlink and their
associated parameters.

The array is composed from both policers that are currently bound to
exposed trap groups and policers that are not bound to any trap group.

v2:
* Provide max/min rate/burst size when registering policers

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