net/mlx5: Wait for FW readiness before initializing command interface

Before attempting to initialize the command interface we must wait till
the fw_initializing bit is clear.

If we fail to meet this condition the hardware will drop our
configuration, specifically the descriptors page address.  This scenario
can happen when the firmware is still executing an FLR flow and did not
finish yet so the driver needs to wait for that to finish.

Fixes: e3297246

 ('net/mlx5_core: Wait for FW readiness on startup')
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>