Use static objects for struct rttimer_queue instead of dynamically

Use static objects for struct rttimer_queue instead of dynamically
allocate them.

Currently there are 6 rttimer_queues and not many more will follow. So
change rt_timer_queue_create() to rt_timer_queue_init() which now takes
a struct rttimer_queue * as argument which will be initialized.
Since this changes the gloabl vars from pointer to struct adjust other
callers as well.
OK bluhm@