x86: coreboot: Wrap cros_ec initialization

cros_ec_board_init() should be called only when CONFIG_CROS_EC is
enabled.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

board/coreboot/coreboot/coreboot.c

@@ -10,8 +10,10 @@
 
 int arch_early_init_r(void)
 {
+#ifdef CONFIG_CROS_EC
 	if (cros_ec_board_init())
 		return -1;
+#endif
 
 	return 0;
 }