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/ti/ks2_evm/board.c b/board/ti/ks2_evm/board.c
index c6735d3..4854771 100644
--- a/board/ti/ks2_evm/board.c
+++ b/board/ti/ks2_evm/board.c
@@ -75,7 +75,7 @@
 	return 0;
 }
 
-#ifdef CONFIG_SPL_BUILD
+#ifdef CONFIG_XPL_BUILD
 void spl_board_init(void)
 {
 	spl_init_keystone_plls();