ice: Add helper to determine if VF link is up

The check for vf->link_up is incorrect because this field is only valid if
vf->link_forced is true. Fix this by adding the helper ice_is_vf_link_up()
to determine if the VF's link is up.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>