KVM: Fix compilation on non-x86

Commit 84b058d7 broke compilation for KVM on non-x86 targets, which
don't have KVM_CAP_IRQ_ROUTING defined.

Fix by not using the unavailable constant when it's not around.
Signed-off-by: NAlexander Graf <agraf@suse.de>

kvm-all.c

@@ -1306,7 +1306,11 @@ int kvm_has_many_ioeventfds(void)
 
 int kvm_has_gsi_routing(void)
 {
+#ifdef KVM_CAP_IRQ_ROUTING
     return kvm_check_extension(kvm_state, KVM_CAP_IRQ_ROUTING);
+#else
+    return false;
+#endif
 }
 
 int kvm_allows_irq0_override(void)