build: always link device_tree.o into emulators if libfdt available

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/Makefile.target b/Makefile.target
index ca657b3..2bd6d14 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -111,6 +111,7 @@
 obj-y += arch_init.o cpus.o monitor.o gdbstub.o balloon.o ioport.o
 obj-y += qtest.o
 obj-y += hw/
+obj-$(CONFIG_FDT) += device_tree.o
 obj-$(CONFIG_KVM) += kvm-all.o
 obj-$(CONFIG_NO_KVM) += kvm-stub.o
 obj-y += memory.o savevm.o cputlb.o