ixgbevf: update Kconfig description

This patch updates the ixgbevf Kconfig description, as the VF driver supports
more than just the 82599 device. This patch renames the config menu item, as
well as updates the help description to make it more obvious that the driver
supports more than just a single device group.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>