generic-board: allow showing custom board info

Allow showing custom board info from a checkboard() function being
implemented if CONFIG_CUSTOM_BOARDINFO is specified.  Previously the
device tree model was always displayed not taking any
CONFIG_CUSTOM_BOARDINFO into account.
Signed-off-by: NMarcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

common/board_info.c

@@ -17,7 +17,7 @@ int __weak checkboard(void)
  */
 int show_board_info(void)
 {
-#ifdef CONFIG_OF_CONTROL
+#if defined(CONFIG_OF_CONTROL) && !defined(CONFIG_CUSTOM_BOARDINFO)
 	DECLARE_GLOBAL_DATA_PTR;
 	const char *model;