board: Use CONFIG_XPL_BUILD instead of CONFIG_SPL_BUILD

Use the new symbol to refer to any 'SPL' build, including TPL and VPL

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/gardena/smart-gateway-mt7688/board.c b/board/gardena/smart-gateway-mt7688/board.c
index eb7fcd6..b6c0fe9 100644
--- a/board/gardena/smart-gateway-mt7688/board.c
+++ b/board/gardena/smart-gateway-mt7688/board.c
@@ -295,7 +295,7 @@
 	return ret;
 }
 
-#ifndef CONFIG_SPL_BUILD
+#ifndef CONFIG_XPL_BUILD
 U_BOOT_CMD(
 	fd_write,	1,	0,	do_fd_write,
 	"Write test factory-data values to SPI NOR",