Adding support for combining DTBs

  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

config.ini

 [common]
-# Possible values for image_type are 1. efi or 2. dtb
-image_type = efi
-# Possible values for file_path are 1. remote or 2. local
+# Section - 1: Common Selection
+# Select operation: 1. sign_image or 2. combine_dtb
+operation = combine_dtb
+# This option is useful for both operations(sign_image & combine_dtb). Possible values for file_path are 1. remote or 2. local
 file_path = local
+# This option is required for both operations(sign_image & combine_dtb) if file_path == remote
 local_machine_private_key_path = /usr2/<user_name_for_machine>/.ssh/id_rsa
+
+# Section - 2: operation == sign_image related common selection
+# Possible values for image_type are 1. efi or 2. dtb
+image_type = efi
+# This option is required if operation == sign_image & image_type == efi
 loader_conf_timeout = 20
 
+# Section - 3: operation == combine_dtb related common selection
+# Possible values for combine_dtb_type are 1. combine_with_old_dtb, 2. combine_without_old_dtb
+combine_dtb_type = combine_with_old_dtb
+
+# Below options are required to fetch file from remote linux machine in the same network(i.e. if file_path == remote)
+
+# This option is useful if operation == sign_image & image_type == efi
 [efi_config]
 efi_remote_hostname = <remotemachine_ip_or_hostname_where_efi.bin_available>
 efi_remote_username = <username_on_remote_machine_where_efi.bin_available>
 efi_remote_filepath = <full_path_of_efi.bin_file_on_remotemachine>
 
+# This option is useful if operation == sign_image. Both image_type requires this option
 [keys_config]
 keys_remote_hostname = <remotemachine_ip_or_hostname_where_keys_available>
 keys_remote_username = <username_on_remote_machine_where_keys_available>
 keys_remote_filepath = <full_path_of_keys_directory_on_remotemachine>
 
+# This option is useful if operation == sign_image & image_type == dtb
 [dtb_config]
 dtb_remote_hostname = <remotemachine_ip_or_hostname_where_dtb_available>
 dtb_remote_username = <username_on_remote_machine_where_dtb_available>
 dtb_remote_filepath = <full_path_of_dtb_on_remotemachine>
 
+# This option is useful if operation == combine_dtb.
+[combine_dtb_config]
+combine_dtb_remote_hostname = <remotemachine_ip_or_hostname_where_combined-dtb.dtb_available>
+combine_dtb_remote_username = <username_on_remote_machine_where_combined-dtb.dtb_available>
+combine_dtb_remote_filepath = <full_path_of_combined-dtb.dtb_on_remotemachine>