arch: 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/arch/arm/mach-imx/mx6/clock.c b/arch/arm/mach-imx/mx6/clock.c
index fb9f56d..b5aa606 100644
--- a/arch/arm/mach-imx/mx6/clock.c
+++ b/arch/arm/mach-imx/mx6/clock.c
@@ -1367,7 +1367,7 @@
 }
 #endif
 
-#ifndef CONFIG_SPL_BUILD
+#ifndef CONFIG_XPL_BUILD
 /*
  * Dump some core clockes.
  */