kvm: x86: Fix -Wmissing-prototypes warnings

We get a warning when build kernel W=1:

arch/x86/kvm/../../../virt/kvm/eventfd.c:48:1: warning: no previous prototype for ‘kvm_arch_irqfd_allowed’ [-Wmissing-prototypes]
 kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args)
 ^

The reason is kvm_arch_irqfd_allowed() is declared in arch/x86/kvm/irq.h,
which is not included by eventfd.c. Considering kvm_arch_irqfd_allowed()
is a weakly defined function in eventfd.c, remove the declaration to
kvm_host.h can fix this.
Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/irq.h

@@ -114,7 +114,6 @@ static inline int irqchip_in_kernel(struct kvm *kvm)
 	return mode != KVM_IRQCHIP_NONE;
 }
 
-bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args);
 void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu);
 void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu);
 void kvm_apic_nmi_wd_deliver(struct kvm_vcpu *vcpu);

include/linux/kvm_host.h

@@ -993,6 +993,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
 				   struct kvm_irq_ack_notifier *kian);
 int kvm_request_irq_source_id(struct kvm *kvm);
 void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id);
+bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args);
 
 /*
  * search_memslots() and __gfn_to_memslot() are here because they are