ice: enable/disable switchdev when managing VFs

Only way to enable switchdev is to create VFs when the eswitch
mode is set to switchdev. Check if correct mode is set and
enable switchdev in function which creating VFs.

Disable switchdev when user change number of VFs to 0. Changing
eswitch mode back to legacy when VFs are created in switchdev
mode isn't allowed.

As switchdev takes care of managing filter rules, adding new
rules on VF is blocked.

In case of resetting VF driver has to update pointer in ice_repr
struct, because after reset VSI related things can change.

Co-developed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Grzegorz Nitka <grzegorz.nitka@intel.com>
Tested-by: Sandeep Penigalapati <sandeep.penigalapati@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>