bootstd: Add support for bootflows

Add support for bootflows, including maintaining a list of them and
iterating to find them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 7b6aada..24e2ad7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -696,8 +696,9 @@
 BOOTDEVICE
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained
-F:	boot/bootmeth*.c
 F:	boot/bootdev*.c
+F:	boot/bootflow.c
+F:	boot/bootmeth*.c
 F:	boot/bootstd.c
 F:	include/bootdev*.h
 F:	include/bootflow.h