net/mlx5: SRIOV core code refactoring

Simplify the code and makes it look modular and symmetric.
Split sriov enable/disable to two levels: device level and pci level.
When user enable/disable sriov (via sriov_configure driver callback) we
will enable/disable both device and pci sriov.
When driver load/unload we will enable/disable (on demand) only device
sriov while keeping the PCI sriov enabled for next driver load.
On internal/pci error, VFs will be kept enabled on PCI and the reset
is done only in device level.

Signed-off-by: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>