Fix build without CONFIG_XEN_EMU

Upstream commit ddf0fd9 "hw/xen: Support HVM_PARAM_CALLBACK_TYPE_GSI callback"
added kvm_xen_maybe_deassert_callback usage to target/i386/kvm/kvm.c file without
conditional preprocessing check. This breaks any build not using CONFIG_XEN_EMU.

Protect call by conditional preprocessing to allow build without CONFIG_XEN_EMU.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20230308130557.2420-1-mrezanin@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm/kvm.c

@@ -4991,6 +4991,7 @@ MemTxAttrs kvm_arch_post_run(CPUState *cpu, struct kvm_run *run)
         kvm_rate_limit_on_bus_lock();
     }
 
+#ifdef CONFIG_XEN_EMU    
     /*
      * If the callback is asserted as a GSI (or PCI INTx) then check if
      * vcpu_info->evtchn_upcall_pending has been cleared, and deassert
@@ -5001,6 +5002,7 @@ MemTxAttrs kvm_arch_post_run(CPUState *cpu, struct kvm_run *run)
     if (x86_cpu->env.xen_callback_asserted) {
         kvm_xen_maybe_deassert_callback(cpu);
     }
+#endif
 
     /* We need to protect the apic state against concurrent accesses from
      * different threads in case the userspace irqchip is used. */