Use separated images for fixed flash layout

For fixed flash layout code update, it was using the whole image-bmc.
For future features like image verification during boot, it needs to use
separated images and separated keys.

So change the image-bmc to separated images.

Change-Id: I6cc56f82c786125bb4386af5ea1d931afed7901d
Tested: Do code update on Romulus without issue.
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/static/flash.cpp b/static/flash.cpp
index 3ca7bfc..6fc4563 100644
--- a/static/flash.cpp
+++ b/static/flash.cpp
@@ -21,7 +21,7 @@
 
 void Activation::flashWrite()
 {
-    // For static layout code update, just put image in /run/initramfs.
+    // For static layout code update, just put images in /run/initramfs.
     // It expects user to trigger a reboot and an updater script will program
     // the image to flash during reboot.
     fs::path uploadDir(IMG_UPLOAD_DIR);