KVM:EVENTFD: fix implicit declaration on x86/_64

During compilation for x86 and x86_64, received the following warning:

virt/kvm/eventfd.c:493:2: error:
 implicit declaration of function 'kvm_vcpu_request_scan_ioapic'
 [-Werror=implicit-function-declaration]
  kvm_vcpu_request_scan_ioapic(kvm);

In the kernel.org linux-stable tree,
commit 29f1b65 KVM:EVENTFD: Remove inclusion of irq.h
by Christoffer Dall addresses this issue.
This backport incudes those portions of that patch which
are relevant in the 3.14 tree.

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Gary S. Robertson <gary.robertson@linaro.org>
Signed-off-by: Kevin Hilman <khilman@linaro.org>
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 0ab1411..ce3ca4c 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -36,6 +36,9 @@
 #include <linux/seqlock.h>
 #include <trace/events/kvm.h>
 
+#ifdef __KVM_HAVE_IOAPIC
+#include "ioapic.h"
+#endif
 #include "iodev.h"
 
 #ifdef CONFIG_HAVE_KVM_IRQFD