net/mlx5: Disable SRIOV before PF removal

Virtual functions depend on physical function for device access (for example
firmware host PAGE management), so make sure to disable SR-IOV once PF is gone.

This will prevent also the below warning if PF has gone before disabling SR-IOV.
"driver left SR-IOV enabled after remove"

Next patch from this series will rely on that when the VF may need to
access safely the PF 'driver data'.

Link: https://lore.kernel.org/all/20220224142024.147653-4-yishaih@nvidia.com
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>