kvm: fix warning for CONFIG_HAVE_KVM_EVENTFD builds

kvm: fix warning for CONFIG_HAVE_KVM_EVENTFD builds

BugLink: http://bugs.launchpad.net/bugs/1786352
[ Upstream commit 076467490b8176eb96eddc548a14d4135c7b5852 ]

Move the kvm_arch_irq_routing_update() prototype outside of
ifdef CONFIG_HAVE_KVM_EVENTFD guards to fix the following sparse warning:

arch/s390/kvm/../../../virt/kvm/irqchip.c:171:28: warning: symbol 'kvm_arch_irq_routing_update' was not declared. Should it be static?

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>