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/configs/mt7628.h b/include/configs/mt7628.h
index 1df0681..ba876ac 100644
--- a/include/configs/mt7628.h
+++ b/include/configs/mt7628.h
@@ -13,7 +13,7 @@
 #define CFG_SYS_INIT_SP_OFFSET		0x80000
 
 /* Serial SPL */
-#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_SERIAL)
+#if defined(CONFIG_XPL_BUILD) && defined(CONFIG_SPL_SERIAL)
 #define CFG_SYS_NS16550_CLK		40000000
 #define CFG_SYS_NS16550_COM1		0xb0000c00
 #endif