net/mlx5e: Check for BlueFlame capability before allocating SQ uar

Previous to this patch mapping was always set to write combining without
checking whether BlueFlame is supported in the device.

Fixes: 0ba42241

 ('net/mlx5: Fix global UAR mapping')
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>