Changeset : initial digic 6 support, sx280 port from srsa_4c in ...

initial digic 6 support, sx280 port from srsa_4c in ​http://chdk.setepontos.com/index.php?topic=12133.msg124275#msg124275

Notes:

• camera_list.csv format is changed
  
• Building in the CHDKShell GUI will be broken. Building form the command prompt launched by CHDKShell should work.
  
• SX280 is not included in the autobuild
  
• Building digic 6 requires GCC 4.8 or later, with OPT_USE_GCC_EABI=1