bootstd: Allow storing the OS command line in the bootflow

Some operating systems have a command line which can be adjusted before
booting. Store this in the bootflow so it can be controlled within
U-Boot.

Fix up the example output while we are here, since there are a few new
items.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/test/boot/bootflow.c b/test/boot/bootflow.c
index 2b5f87d..f7ebf9d 100644
--- a/test/boot/bootflow.c
+++ b/test/boot/bootflow.c
@@ -226,6 +226,7 @@
 	ut_assert_nextlinen("Buffer:    ");
 	ut_assert_nextline("Size:      253 (595 bytes)");
 	ut_assert_nextline("OS:        Fedora-Workstation-armhfp-31-1.9 (5.3.7-301.fc31.armv7hl)");
+	ut_assert_nextline("Cmdline:   (none)");
 	ut_assert_nextline("Logo:      (none)");
 	ut_assert_nextline("FDT:       <NULL>");
 	ut_assert_nextline("Error:     0");