firmware: add verification response enum

Add verification response enum per the design spec.

Change-Id: I7ecb388312798210ec768c134a4454dfceb7866b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/firmware_handler.hpp b/firmware_handler.hpp
index 46497e3..30b450b 100644
--- a/firmware_handler.hpp
+++ b/firmware_handler.hpp
@@ -73,6 +73,15 @@
         verificationCompleted = 3,
     };
 
+    /** The return values for verification. */
+    enum VerifyCheckResponses : std::uint8_t
+    {
+        running = 0,
+        success = 1,
+        failed = 2,
+        other = 3,
+    };
+
     /**
      * Create a FirmwareBlobHandler.
      *