toradex: Use checkboard() instead of show_board_info()

Boards can use a sysinfo driver if a particular model name is needed.
Update this board to use checkboard() directly, rather than having a
weak function laid on top of a weak function.

Make all the checkboard() functions call the new tdx_checkboard() so
that the same information is displayed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/toradex/colibri-imx6ull/colibri-imx6ull.c b/board/toradex/colibri-imx6ull/colibri-imx6ull.c
index 48fdb1e..6c8eeff 100644
--- a/board/toradex/colibri-imx6ull/colibri-imx6ull.c
+++ b/board/toradex/colibri-imx6ull/colibri-imx6ull.c
@@ -206,7 +206,7 @@
 {
 	printf("Model: Toradex Colibri iMX6ULL\n");
 
-	return 0;
+	return tdx_checkboard();
 }
 
 #if defined(CONFIG_OF_LIBFDT) && defined(CONFIG_OF_BOARD_SETUP)