stubs: add ramfb

Needed to make sure code using ramfb (vfio) compiles properly even on
platforms without fw_cfg (and therefore no ramfb) support.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

stubs/Makefile.objs

@@ -43,3 +43,4 @@ 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
+stub-obj-y += ramfb.o

stubs/ramfb.c

@@ -0,0 +1,13 @@
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "hw/display/ramfb.h"
+
+void ramfb_display_update(QemuConsole *con, RAMFBState *s)
+{
+}
+
+RAMFBState *ramfb_setup(Error **errp)
+{
+    error_setg(errp, "ramfb support not available");
+    return NULL;
+}