KVM: Add CONFIG_HAVE_KVM_IRQCHIP

Two KVM archs support irqchips and two don't.  Add a Kconfig item to
make selecting between the two models easier.

Signed-off-by: Avi Kivity <avi@redhat.com>

arch/ia64/kvm/Kconfig

@@ -4,6 +4,10 @@
 config HAVE_KVM
 	bool
 
+config HAVE_KVM_IRQCHIP
+       bool
+       default y
+
 menuconfig VIRTUALIZATION
 	bool "Virtualization"
 	depends on HAVE_KVM || IA64