firmware: move enum into class

This will protect the namespace from pollution, but also allow it to be
just a normal enum for arithmetic operations.

Change-Id: Ie4eab4040619b0c37ab0395b984437ebf3cf2101
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/firmware_canhandle_unittest.cpp b/test/firmware_canhandle_unittest.cpp
index b82ab6a..028d472 100644
--- a/test/firmware_canhandle_unittest.cpp
+++ b/test/firmware_canhandle_unittest.cpp
@@ -27,7 +27,7 @@
     };
 
     auto handler = FirmwareBlobHandler::CreateFirmwareBlobHandler(
-        blobs, static_cast<uint16_t>(FirmwareUpdateFlags::bt));
+        blobs, FirmwareBlobHandler::FirmwareUpdateFlags::bt);
 
     for (const auto& item : items)
     {