ixgbevf: Kconfig, Makefile and Documentation

Modifications for the Kconfig and network device Makefile to add the ixgbevf
driver module to the kernel plus basic driver documentation.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>