spl: Support a relocated stack in any XPL phase

The current check looks only at SPL, but TPL or VPL might have a
different setting. Update the condition.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 91ee07f..702920b 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -896,7 +896,7 @@
  */
 ulong spl_relocate_stack_gd(void)
 {
-#ifdef CONFIG_SPL_STACK_R
+#if CONFIG_IS_ENABLED(STACK_R)
 	gd_t *new_gd;
 	ulong ptr = CONFIG_SPL_STACK_R_ADDR;