cpumask: remove cpumask_t from core

Impact: cleanup

struct cpumask is nicer, and we use it to make where we've made code
safe for CONFIG_CPUMASK_OFFSTACK=y.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

kernel/sched_cpupri.h

@@ -25,7 +25,7 @@ struct cpupri {
 
 #ifdef CONFIG_SMP
 int  cpupri_find(struct cpupri *cp,
-		 struct task_struct *p, cpumask_t *lowest_mask);
+		 struct task_struct *p, struct cpumask *lowest_mask);
 void cpupri_set(struct cpupri *cp, int cpu, int pri);
 int cpupri_init(struct cpupri *cp, bool bootmem);
 void cpupri_cleanup(struct cpupri *cp);

kernel/stop_machine.c

@@ -44,7 +44,7 @@ static DEFINE_MUTEX(setup_lock);
 static int refcount;
 static struct workqueue_struct *stop_machine_wq;
 static struct stop_machine_data active, idle;
-static const cpumask_t *active_cpus;
+static const struct cpumask *active_cpus;
 static void *stop_machine_work;
 
 static void set_state(enum stopmachine_state newstate)