include: Add stubbed xen function

Will allow us to not comment out code all the time for xen checks (ideally)

qemu/include/exec/ram_addr.h

@@ -22,6 +22,7 @@
 #include "uc_priv.h"
 
 #ifndef CONFIG_USER_ONLY
+#include "hw/xen/xen.h"
 
 ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
                                    MemoryRegion *mr, Error **errp);

qemu/include/hw/xen/xen.h

@@ -0,0 +1,13 @@
+#ifndef QEMU_HW_XEN_H
+#define QEMU_HW_XEN_H
+
+#include "qemu-common.h"
+#include "exec/cpu-common.h"
+
+static inline bool xen_enabled(void)
+{
+    // Unicorn: Always return false
+    return false;
+}
+
+#endif