stubs: Add stubs for ram block API

These functions will be wanted by block-obj-y but the actual definition
is in obj-y, so stub them to keep the linker happy.

Signed-off-by: Fam Zheng <famz@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20180110091846.10699-2-famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

stubs/Makefile.objs

@@ -42,3 +42,4 @@ stub-obj-y += vmgenid.o
 stub-obj-y += xen-common.o
 stub-obj-y += xen-hvm.o
 stub-obj-y += pci-host-piix.o
+stub-obj-y += ram-block.o

stubs/ram-block.c

+#include "qemu/osdep.h"
+#include "exec/ramlist.h"
+#include "exec/cpu-common.h"
+
+void ram_block_notifier_add(RAMBlockNotifier *n)
+{
+}
+
+void ram_block_notifier_remove(RAMBlockNotifier *n)
+{
+}
+
+int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque)
+{
+    return 0;
+}