bootstage: Convert to use malloc()

At present bootstage uses the data section of the image to store its
information. There are a few problems with this:

- It does not work on all boards (e.g. those which run from flash before
relocation)
- Allocated strings still point back to the pre-relocation data after
relocation

Now that U-Boot has a pre-relocation malloc() we can use this instead,
with a pointer to the data in global_data. Update bootstage to do this and
set up an init routine to allocate the memory.

Now that we have a real init function, we can drop the fake 'reset' record
and add a normal one instead.

Note that part of the problem with allocated strings remains. They are
reallocated but this will only work where pre-relocation memory is
accessible after relocation.

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

include/bootstage.h

@@ -331,6 +331,14 @@ int bootstage_stash(void *base, int size);
  */
 int bootstage_unstash(void *base, int size);
 
+/**
+ * bootstage_init() - Prepare bootstage for use
+ *
+ * @first: true if this is the first time bootstage is set up. This causes it
+ *	to add a 'reset' record with a time of 0.
+ */
+int bootstage_init(bool first);
+
 #else
 static inline ulong bootstage_add_record(enum bootstage_id id,
 		const char *name, int flags, ulong mark)
@@ -391,6 +399,11 @@ static inline int bootstage_unstash(void *base, int size)
 {
 	return 0;	/* Pretend to succeed */
 }
+
+static inline int bootstage_init(bool first)
+{
+	return 0;
+}
 #endif /* CONFIG_BOOTSTAGE */
 
 /* Helper macro for adding a bootstage to a line of code */