o Added new operation of combining DTBs
    - Script can either sign images or combine DTBs
    - For combining DTBs there are two options
      - Combine dtb files with old dtb.bin data
      - No dtb.bin - only combine dtb files and create new dtb.bib
  o Updated config.ini file accordingly
  o Updated script general messages
  o Updated script functionalities
    - select operation support with API
    - copy dtb from remote machine
    - Append data from old dtb.bin + dtb files to combine dtb file
    - Create dtb.bin(vfat) file and copy new combined dtb to it

Change-Id: I409a39f02f57ba8aa07218cd4bc29d17ab21a2c7