net/mlx4: New file for QoS related firmware commands

Create two new files fw_qos.h and fw_qos.c in mlx4_core module.

It gathers all relevant QoS firmware related commands etc, thus improving
encapsulation of the mlx4_core module. For now it contains the QoS existing
commands: mlx4_SET_PORT_SCHEDULER and mlx4_SET_PORT_PRIO2TC.

Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>