firmwarehandler: Provide a factory for building

Provide a factory for building the firmware blob handler.  This allows
us to later provide built-time parameters to the handler through the
constructor and not within the object itself.

Change-Id: I19c90de45eaf65b78dfd55beb61f2ad4cc6fa43e
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/main.cpp b/main.cpp
index 127d37b..b7d35d1 100644
--- a/main.cpp
+++ b/main.cpp
@@ -13,7 +13,8 @@
 void setupFirmwareHandler()
 {
     auto* manager = getBlobManager();
-    if (!manager->registerHandler(std::make_unique<FirmwareBlobHandler>()))
+    if (!manager->registerHandler(
+            FirmwareBlobHandler::CreateFirmwareBlobHandler()))
     {
         log<level::ERR>("Failed to register Firmware Handler");
     }