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/kontron/sl28/ddr.c b/board/kontron/sl28/ddr.c
index 9b881fd..1f1a6aa 100644
--- a/board/kontron/sl28/ddr.c
+++ b/board/kontron/sl28/ddr.c
@@ -98,7 +98,7 @@
 		break;
 	}
 
-	if (!IS_ENABLED(CONFIG_SPL) || IS_ENABLED(CONFIG_SPL_BUILD))
+	if (!IS_ENABLED(CONFIG_SPL) || IS_ENABLED(CONFIG_XPL_BUILD))
 		fsl_ddr_set_memctl_regs(&ddr_cfg_regs, 0, 0);
 
 	gd->ram_size = dram_size;