intel/haswell: add vmx support w/Kconfig option

patch based on VMX support in intel/fsp_model_206ax and intel/model_6fx
tested/verified working on google/panther

Change-Id: I61232fdc2a29c53aa3bea5ea78b2fdc41fd7396a
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: http://review.coreboot.org/6223
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>