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/power/regulator/rk8xx.c b/drivers/power/regulator/rk8xx.c
index 34e6151..3f18ee6 100644
--- a/drivers/power/regulator/rk8xx.c
+++ b/drivers/power/regulator/rk8xx.c
@@ -16,7 +16,7 @@
 #include <power/pmic.h>
 #include <power/regulator.h>
 
-#ifndef CONFIG_SPL_BUILD
+#ifndef CONFIG_XPL_BUILD
 #define ENABLE_DRIVER
 #endif