mlxsw: reg: Move enum mlxsw_reg_ratr_trap_id

This enum is used with reg_ratr_trap_id, so move it next to the register
definition.

While at it, drop the enumerator initializers.

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