[power] Divorce suspend console code from swsusp.

[power] Divorce suspend console code from swsusp.

- Create kernel/power/console.c
- Rename prepare_suspend_console() to pm_prepare_console() and
  restore_console() to pm_restore_console().
- Add prototypes to include/linux/suspend.h.
- Make kernel/power/console.o dependent only on CONFIG_PM
- Simplify logic for SUSPEND_CONSOLE define
- Make software_resume() prepare console much earlier, so we can localize
  the loglevel variables in console.c.
- Remove #ifdef CONFIG_VT from console.c, and just check for SUSPEND_CONSOLE.
  (Perhaps we should make entire file dependent on CONFIG_VT_CONSOLE?)
- Add kernel/power/power.h to share things across local files.