net/mlx5e: Single bfreg (UAR) for all mlx5e SQs and netdevs

One is sufficient since Blue Flame is not supported anymore.
This will also come in handy for switchdev mode to save resources, since
VF representors will use same single UAR as well for their own SQs.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>