item_updater: sort ubi specific code

Add item_updater_helper and implement it in ubi and static layouts.

Tested: Build this repo on both Romulus and Witherspoon OK;
        Tested on Romulus and Witherspoon that code update works fine.

Change-Id: I706cfe63900f89bb41672dcc745b3483e06838c7
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/Makefile.am b/Makefile.am
index 1ac3914..18c8763 100755
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,9 @@
 	images.hpp \
 	image_manager.hpp \
 	item_updater.hpp \
-	activation.hpp
+	activation.hpp \
+	flash.hpp \
+	item_updater_helper.hpp
 
 sbin_PROGRAMS = \
 	phosphor-version-software-manager \