bootstd: Allow scanning for global bootmeths separately

Typically we want to find and use global bootmeths first, since they have
the best idea of how the system should boot. We then use normal bootmeths
as a fallback.

Add the logic for this, putting global bootmeths at the end of the
ordering. We can then easily scan the global bootmeths first, then drop
them from the list for subsequent bootdev-centric scans.

This changes the ordering of global bootmeths, so update the
bootflow_system() accordingly.

Drop the comment from bootmeth_setup_iter_order() since this is an
exported function and it should be in the header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/bootmeth.h b/include/bootmeth.h
index c93367b..50ded05 100644
--- a/include/bootmeth.h
+++ b/include/bootmeth.h
@@ -209,10 +209,12 @@
  * ordering there, then all bootmethods are added
  *
  * @iter: Iterator to update with the order
+ * @include_global: true to add the global bootmeths, in which case they appear
+ * first
  * Return: 0 if OK, -ENOENT if no bootdevs, -ENOMEM if out of memory, other -ve
  *	on other error
  */
-int bootmeth_setup_iter_order(struct bootflow_iter *iter);
+int bootmeth_setup_iter_order(struct bootflow_iter *iter, bool include_global);
 
 /**
  * bootmeth_set_order() - Set the bootmeth order