mlxsw: reg: Add QoS ETS Element Configuration register

We are going to introduce support for DCB, so we need to be able to
configure the traffic selection algorithm (TSA) used by each traffic
class (TC), as well as the bandwidth percentage allocated to each TC in
case of ETS.

Add the QoS ETS Element Configuration register, which controls the
above parameters.

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