Rather than passing the vm type from the top level to the end of vm
creation, let's simply keep that as an internal of kvm_vm struct and
decide the type in _vm_create().  Several reasons for doing this:

- The vm type is only decided by physical address width and currently
  only used in aarch64, so we've got enough information as long as
  we're passing vm_guest_mode into _vm_create(),

- This removes a loop dependency between the vm->type and creation of
  vms.  That's why now we need to parse vm_guest_mode twice sometimes,
  once in run_test() and then again in _vm_create().  The follow up
  patches will move on to clean up that as well so we can have a
  single place to decide guest machine types and so.

Note that this patch will slightly change the behavior of aarch64
tests in that previously most vm_create() callers will directly pass
in type==0 into _vm_create() but now the type will depend on
vm_guest_mode, however it shouldn't affect any user because all
vm_create() users of aarch64 will be using VM_MODE_DEFAULT guest
mode (which is VM_MODE_P40V48_4K) so at last type will still be zero.
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>