i40evf: Move some i40evf_reset_task code to separate function

The i40evf_reset_task function is a couple hundred lines and it has
a separable block that disables VF.  Move that block to a new
i40evf_disable_vf function to shorten i40evf_reset_task a bit.

Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>