Add a 16-bytes buffer to allow storing a 128-bit UUID value in an
ACPI table.

Signed-off-by: Gal Hammer <ghammer@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>