net/mlx5: Read embedded cpu bit only once

Embedded CPU bit doesn't change with PCI resume/suspend.
Hence read it only once while probing the PCI device.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>