net/mlx5: Split function_setup() to enable and open functions

mlx5_cmd_init_hca() is taking ~0.2 seconds. In case of a user who
desire to disable some of the SF aux devices, and with large scale-1K
SFs for example, this user will waste more than 3 minutes on
mlx5_cmd_init_hca() which isn't needed at this stage.

Downstream patch will change SFs which are probe over the E-switch,
local SFs, to be probed without any aux dev. In order to support this,
split function_setup() to avoid executing mlx5_cmd_init_hca().

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>