leds: change existing triggers to use activated flag

Change existing triggers backlight, gpio, and heartbeat to use the new
->activated flag to set activate successful status in their activate
routines and check it in their deactivate routines to do cleanup.

Signed-off-by: Shuah Khan <shuahkhan@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>