include: 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/include/vbe.h b/include/vbe.h
index 5ede818..56bff63 100644
--- a/include/vbe.h
+++ b/include/vbe.h
@@ -41,7 +41,7 @@
  */
 static inline enum vbe_phase_t vbe_phase(void)
 {
-	if (IS_ENABLED(CONFIG_SPL_BUILD))
+	if (IS_ENABLED(CONFIG_XPL_BUILD))
 		return VBE_PHASE_FIRMWARE;
 
 	return VBE_PHASE_OS;