bootstd: Read the Operating System name for distro/scripts

Add the concept of an OS name to the bootflow. This typically includes the
OS name, version and kernel version.

Implement this for the distro and script bootmeths so that it works with
Armbian and older version of Fedora.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/bootflow.c b/boot/bootflow.c
index f9ad409..163cd49 100644
--- a/boot/bootflow.c
+++ b/boot/bootflow.c
@@ -354,6 +354,7 @@
 	free(bflow->subdir);
 	free(bflow->fname);
 	free(bflow->buf);
+	free(bflow->os_name);
 }
 
 void bootflow_remove(struct bootflow *bflow)