- Move definition of struct pmdsik_info to power.h and rename to struct 
  swsusp_info.
- Kill struct suspend_header. 
- Move helpers from pmdisk into swsusp: init_header(), dump_info(), 
  write_header(), sanity_check(), check_header().
- Fix up calls in pmdisk to call the right ones. 
- Clean up swsusp code to use helpers; delete duplicates.