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/powerpc/kvm/Kconfig

@@ -2,6 +2,9 @@
 # KVM configuration
 #
 
+config HAVE_KVM_IRQCHIP
+       bool
+
 menuconfig VIRTUALIZATION
 	bool "Virtualization"
 	---help---