klist: implement KLIST_INIT() and DEFINE_KLIST()

klist is missing static initializers and definition helper.  Add them.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>