move files around to create a common convenience library

Problem: plan is to add another blob handler into ipmi-flash
(ipmi-flash-version). This new handler will re-use much of the
ipmi-flash (firmware-handler) code. The common code should be presented
as a convenience library to reduce code duplication.

Solution: move anticipated firmware-handler specific code into the
subdirectory bmc/firmware-handler and leave common code in bmc/.

The end goal is to have version-handler re-use as
much code as possible.

Tested:
rebuilt everything and ran unit tests.

Signed-off-by: Jason Ling <jasonling@google.com>
Change-Id: I2128da629b0ddf27b89f1faee358d1941f1dff38
diff --git a/bmc/image_handler.hpp b/bmc/image_handler.hpp
index a25a74a..c024ec9 100644
--- a/bmc/image_handler.hpp
+++ b/bmc/image_handler.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
 #include <cstdint>
-#include <functional>
+#include <fstream>
 #include <memory>
 #include <string>
 #include <vector>