net/mlx5: Do not query MPIR on embedded CPU function

[ Upstream commit fca3b479 ]

A proper query to MPIR needs to set the correct value in the depth field.
On embedded CPU this value is not necessarily zero. As there is no real
use case for multi-PF netdev on the embedded CPU of the smart NIC, block
this option.

This fixes the following failure:
ACCESS_REG(0x805) op_mod(0x1) failed, status bad system state(0x4), syndrome (0x685f19), err(-5)

Fixes: 678eb448

 ("net/mlx5: SD, Implement basic query and instantiation")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>