drivers: 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/drivers/misc/imx8/scu.c b/drivers/misc/imx8/scu.c
index bbd7e24..5d3db0b 100644
--- a/drivers/misc/imx8/scu.c
+++ b/drivers/misc/imx8/scu.c
@@ -191,7 +191,7 @@
 	if (addr == FDT_ADDR_T_NONE)
 		return -EINVAL;
 
-#ifdef CONFIG_SPL_BUILD
+#ifdef CONFIG_XPL_BUILD
 	plat->base = (struct mu_type *)CONFIG_MU_BASE_SPL;
 #else
 	plat->base = (struct mu_type *)addr;