i386: Remove generic SMT thread check

Remove generic non-intel check while validating hyperthreading support.
Certain AMD CPUs can support hyperthreading now.

CPU family with TOPOEXT feature can support hyperthreading now.

Signed-off-by: Babu Moger <babu.moger@amd.com>
Tested-by: Geoffrey McRae <geoff@hostfission.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <1529443919-67509-4-git-send-email-babu.moger@amd.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>