mlxsw: reg: Add max_shaper_bs to QoS ETS Element Configuration

The QEEC register configures scheduling elements. One of the bits of
configuration is the burst size to use for the shaper installed on the
element. Add the necessary fields to support this configuration.

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