s390x: uv: Add UV lib

Lets add a UV library to make checking the UV feature bit easier.
In the future this library file can take care of handling UV
initialization and UV guest creation.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>