kvm: require KVM_IRQFD for kernel irqchip

KVM_IRQFD was introduced in Linux 2.6.32, and since then it has always been
available on architectures that support an in-kernel interrupt controller.
We can require it unconditionally.

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/sysemu/kvm.h

@@ -167,6 +167,7 @@ extern bool kvm_msi_use_devid;
 #define kvm_irqchip_is_split() (false)
 #define kvm_async_interrupts_enabled() (false)
 #define kvm_halt_in_kernel() (false)
+#define kvm_irqfds_enabled() (false)
 #define kvm_eventfds_enabled() (false)
 #define kvm_resamplefds_enabled() (false)
 #define kvm_msi_via_irqfd_enabled() (false)