LGUEST_GUEST: fix unmet direct dependencies (VIRTUALIZATION && VIRTIO)

Honor the kconfig menu hierarchy to remove kconfig dependency warnings:
VIRTIO and VIRTIO_RING are subordinate to VIRTUALIZATION.

warning: (LGUEST_GUEST) selects VIRTIO which has unmet direct dependencies (VIRTUALIZATION)
warning: (LGUEST_GUEST && VIRTIO_PCI && VIRTIO_BALLOON) selects VIRTIO_RING which has unmet direct dependencies (VIRTUALIZATION && VIRTIO)
Reported-by: Toralf F_rster <toralf.foerster@gmx.de>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/x86/lguest/Kconfig

@@ -2,6 +2,7 @@ config LGUEST_GUEST
 	bool "Lguest guest support"
 	select PARAVIRT
 	depends on X86_32
+	select VIRTUALIZATION
 	select VIRTIO
 	select VIRTIO_RING
 	select VIRTIO_CONSOLE