Add --describe flag to {firmware|kernel}_utility.

src/platform/vboot_reference/include/kernel_image.h

Index: src/platform/vboot_reference/include/kernel_image.h
diff --git a/src/platform/vboot_reference/include/kernel_image.h b/src/platform/vboot_reference/include/kernel_image.h
index 96c8f256964f238cc58c3191a473738034cd26a1..7c7b16f17e04770f7b108541220d91c57714f750 100644
--- a/src/platform/vboot_reference/include/kernel_image.h
+++ b/src/platform/vboot_reference/include/kernel_image.h
@@ -80,6 +80,15 @@ KernelImage* ReadKernelImage(const char* input_file);
 /* Get the length of the header for kernel image [image]. */
 int GetKernelHeaderLen(const KernelImage* image);
 
+/* Calculate and store the kernel header checksum of [image]
+ * in [header_checksum].
+ *
+ * [header_checksum] must be a valid pointer to a buffer of
+ * SHA512_DIGEST_SIZE.
+ */
+void CalculateKernelHeaderChecksum(const KernelImage* image,
+                                   uint8_t* header_checksum);
+
 /* Get kernel header binary blob from an [image].
  *
  * Caller owns the returned pointer and must Free() it.