[power] Further swsusp cleanups.

[power] Further swsusp cleanups.

- Remove drivers_resume() and call from do_magic_resume2(). Handled by core.
- When bringing devices back to life, call device_pm_resume()
- Make sure we report the error from write_suspend_image()
- Remove suspend_power_down() and call to it. Handled by PM core.
- Move swap file resetting and freeing of pagedir to swsusp_free()
- Remove extraneous in_atomic() checks.
- Mark all resume functions __init.
- Move resume_suspend_image() inside swsusp_read() and cleanup.
- Make do_magic() report error.