clockintr: refactor clockintr_queue initialization into clockqueue_init()

clockintr: refactor clockintr_queue initialization into clockqueue_init()

We need to be able to initialize a given struct clockintr_queue before
clockintr_cpu_init() is called.  This will allow the primary CPU to
establish clock interrupts on other CPUs' queues before those CPUs
have finished booting.

So, move the clockintr_queue structure initialization code out of
clockintr_cpu_init() into a new function, clockqueue_init().
clockqueue_init() sets CQ_INIT the first time it is called.
Subsequent calls do nothing.