It's not useful to build LED triggers when there's no LEDs that can be
triggered by them.  Therefore, fix up the dependencies so that this
cannot happen, and fix a few users that select triggers to depend on
LEDS_CLASS as well (there is also one user that also selects LEDS_CLASS,
which is OK).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Tested-by: Ingo Molnar <mingo@elte.hu>
Cc: Arnd Hannemann <arnd@arndnet.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Richard Purdie <rpurdie@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>