Added recovery-mode return code to LoadKernel()

This will be used if the TPM functions return error.

Review URL: http://codereview.chromium.org/2681003
diff --git a/vboot_firmware/include/load_kernel_fw.h b/vboot_firmware/include/load_kernel_fw.h
index f4c512a..77e5d50 100644
--- a/vboot_firmware/include/load_kernel_fw.h
+++ b/vboot_firmware/include/load_kernel_fw.h
@@ -14,9 +14,10 @@
 /* Interface provided by verified boot library to BDS */
 
 /* Return codes for LoadKernel() */
-#define LOAD_KERNEL_SUCCESS 0
-#define LOAD_KERNEL_NOT_FOUND 1
-#define LOAD_KERNEL_INVALID 2
+#define LOAD_KERNEL_SUCCESS 0    /* Success; good kernel found on device */
+#define LOAD_KERNEL_NOT_FOUND 1  /* No kernel found on device */
+#define LOAD_KERNEL_INVALID 2    /* Only invalid kernels found on device */
+#define LOAD_KERNEL_RECOVERY 3   /* Internal error; reboot to recovery mode */
 
 /* Boot modes for LoadKernel() */
 #define BOOT_MODE_NORMAL 0