bootstage: Add feature to stash/unstash bootstage info

It is useful to be able to write the bootstage information to memory for
use by a later utility, or the Linux kernel. Provide a function to do
this as well as a function to read bootstage information back and incorporate
it into the current table.

This also makes it possible for U-Boot to chain to another U-Boot and pass
on its bootstage information.

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

include/bootstage.h

@@ -284,6 +284,27 @@ void bootstage_report(void);
  */
 int bootstage_fdt_add_report(void);
 
+/*
+ * Stash bootstage data into memory
+ *
+ * @param base	Base address of memory buffer
+ * @param size	Size of memory buffer
+ * @return 0 if stashed ok, -1 if out of space
+ */
+int bootstage_stash(void *base, int size);
+
+/**
+ * Read bootstage data from memory
+ *
+ * Bootstage data is read from memory and placed in the bootstage table
+ * in the user records.
+ *
+ * @param base	Base address of memory buffer
+ * @param size	Size of memory buffer (-1 if unknown)
+ * @return 0 if unstashed ok, -1 if bootstage info not found, or out of space
+ */
+int bootstage_unstash(void *base, int size);
+
 #else
 /*
  * This is a dummy implementation which just calls show_boot_progress(),
@@ -307,7 +328,15 @@ static inline ulong bootstage_mark_name(enum bootstage_id id, const char *name)
 	return 0;
 }
 
+static inline int bootstage_stash(void *base, int size)
+{
+	return 0;	/* Pretend to succeed */
+}
 
+static inline int bootstage_unstash(void *base, int size)
+{
+	return 0;	/* Pretend to succeed */
+}
 #endif /* CONFIG_BOOTSTAGE */
 
 #endif