piegen: opts variable is global

Since opts is defined as extern in piegen.h, there is no need to pass it as
argument.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>