Add support to explicitly disable ENA support
Add support to explicitly disable ENA support

If `ena_support` is set to false then it previously didn't do anything
whereas now it will explicitly disable ENA support.

Fixes #6852

youhong316/packer,timsutton/packer,dave2/packer,mitchellh/packer,paulmey/packer,ricardclau/packer,tb3088/packer,tb3088/packer,dave2/packer,mitchellh/packer,dave2/packer,bryson/packer,tas50/packer,tas50/packer,bryson/packer,hashicorp/packer,tb3088/packer,paulmey/packer,pecigonzalo/packer,hashicorp/packer,ricardclau/packer,mkuzmin/packer,timsutton/packer,pecigonzalo/packer,grubernaut/packer,grubernaut/packer,mitchellh/packer,youhong316/packer,rnaveiras/packer,rnaveiras/packer,tas50/packer,grubernaut/packer,mkuzmin/packer,grubernaut/packer,bryson/packer,tb3088/packer,timsutton/packer,youhong316/packer,youhong316/packer,tb3088/packer,rnaveiras/packer,youhong316/packer,mitchellh/packer,bryson/packer,rnaveiras/packer,bryson/packer,ricardclau/packer,ricardclau/packer,dave2/packer,mitchellh/packer,ricardclau/packer,timsutton/packer,youhong316/packer,pecigonzalo/packer,ricardclau/packer,tas50/packer,tas50/packer,tas50/packer,mkuzmin/packer,dave2/packer,paulmey/packer,hashicorp/packer,timsutton/packer,pecigonzalo/packer,tb3088/packer,mkuzmin/packer,dave2/packer,grubernaut/packer,timsutton/packer,paulmey/packer,mkuzmin/packer,grubernaut/packer,mkuzmin/packer,bryson/packer,rnaveiras/packer,hashicorp/packer,paulmey/packer,paulmey/packer,rnaveiras/packer