pm: remove definition of struct pm_dev

Remove the definition of 'struct pm_dev', which is not used any more,
along with some related stuff from include/linux/pm.h .

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>