[PATCH] LED: add LED timer trigger

Add an example of a complex LED trigger in the form of a generic timer which
triggers the LED its attached to at a user specified frequency and duty cycle.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>