qemu_v8.mk: do not warn about unreadable kernel if XEN_BOOT != y

The readability check of the host kernel makes sense only when
XEN_BOOT=y, so avoid annoying users that are not concerned by this.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Ruchika Gupta <ruchika.gupta@linaro.org>
diff --git a/qemu_v8.mk b/qemu_v8.mk
index 24c4a43..536eea5 100644
--- a/qemu_v8.mk
+++ b/qemu_v8.mk
@@ -346,11 +346,13 @@
 $(XEN_TMP):
 	mkdir -p $@
 
+ifeq ($(XEN_BOOT),y)
 # virt-make-fs needs to be able to read the local kernel
 # See https://bugs.launchpad.net/ubuntu/+source/linux/+bug/759725
 build-host-vmlinuz := $(shell echo /boot/vmlinuz-`uname -r`)
 $(if $(shell [ -r $(build-host-vmlinuz) ] || echo No), \
   $(error $(build-host-vmlinuz) is unreadable. Please run: sudo chmod a+r $(build-host-vmlinuz) and try again))
+endif
 
 xen-create-image: xen linux buildroot | $(XEN_TMP)
 	cp $(KERNEL_IMAGE) $(XEN_TMP)