lguest: now depends on PCI

Reported-by: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

arch/x86/lguest/Kconfig

 config LGUEST_GUEST
 	bool "Lguest guest support"
-	depends on X86_32 && PARAVIRT
+	depends on X86_32 && PARAVIRT && PCI
 	select TTY
 	select VIRTUALIZATION
 	select VIRTIO