bootstd: Allow reading a logo for the OS

Some operating systems provide a logo in bmp format. Read this in if
present so it can be displayed in the menu.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/boot/bootflow.c b/test/boot/bootflow.c
index 3296316..00dfd99 100644
--- a/test/boot/bootflow.c
+++ b/test/boot/bootflow.c
@@ -189,6 +189,7 @@
 	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("Logo:      (none)");
 	ut_assert_nextline("Error:     0");
 	ut_assert_console_end();