x86: Add a default address for reference code

Add an address which can be used for loading and running the reference code
when needed.

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

include/configs/x86-chromebook.h

@@ -14,6 +14,8 @@
 #define CONFIG_MISC_INIT_R
 
 #define CONFIG_X86_MRC_ADDR			0xfffa0000
+#define CONFIG_X86_REFCODE_ADDR			0xffea0000
+#define CONFIG_X86_REFCODE_RUN_ADDR		0
 
 #define CONFIG_SCSI_DEV_LIST	\
 	{PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_NM10_AHCI}, \