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/st/common/cmd_stboard.c b/board/st/common/cmd_stboard.c
index 50da063..b9d0abd 100644
--- a/board/st/common/cmd_stboard.c
+++ b/board/st/common/cmd_stboard.c
@@ -29,7 +29,7 @@
  *   Board: MB<Board> Var<VarCPN>.<VarFG> Rev.<Revision>-<BOM>
  */
 
-#ifndef CONFIG_SPL_BUILD
+#ifndef CONFIG_XPL_BUILD
 #include <command.h>
 #include <console.h>
 #include <misc.h>