KVM: replace direct irq.h inclusion

virt/kvm/irqchip.c is including "irq.h" from the arch-specific KVM source
directory (i.e. not from arch/*/include) for the sole purpose of retrieving
irqchip_in_kernel.

Making the function inline in a header that is already included,
such as asm/kvm_host.h, is not possible because it needs to look at
struct kvm which is defined after asm/kvm_host.h is included.  So add a
kvm_arch_irqchip_in_kernel non-inline function; irqchip_in_kernel() is
only performance critical on arm64 and x86, and the non-inline function
is enough on all other architectures.

irq.h can then be deleted from all architectures except x86.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/kvm_host.h

@@ -663,6 +663,8 @@ struct kvm_irq_routing_table {
 	 */
 	struct hlist_head map[];
 };
+
+bool kvm_arch_irqchip_in_kernel(struct kvm *kvm);
 #endif
 
 #ifndef KVM_INTERNAL_MEM_SLOTS