KVM: S390: Add dummy kvm_arch_init_irq_routing()

The common KVM code insists on calling kvm_arch_init_irq_routing()
as soon as it sees kernel header support for it (regardless of whether
QEMU supports it).  Provide a dummy function to satisfy this.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

target-s390x/kvm.c

@@ -928,3 +928,7 @@ void kvm_s390_enable_css_support(S390CPU *cpu)
     r = kvm_vcpu_ioctl(CPU(cpu), KVM_ENABLE_CAP, &cap);
     assert(r == 0);
 }
+
+void kvm_arch_init_irq_routing(KVMState *s)
+{
+}