bootstage: Store boot timings in device tree

Add an option, CONFIG_BOOTSTAGE_FDT to pass boot timings to the kernel
in the device tree, if available. To use this, you must have
CONFIG_OF_LIBFDT defined.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/bootstage.h

@@ -277,6 +277,13 @@ uint32_t bootstage_accum(enum bootstage_id id);
 /* Print a report about boot time */
 void bootstage_report(void);
 
+/**
+ * Add bootstage information to the device tree
+ *
+ * @return 0 if ok, -ve on error
+ */
+int bootstage_fdt_add_report(void);
+
 #else
 /*
  * This is a dummy implementation which just calls show_boot_progress(),