sched: wrap sched_group and sched_domain cpumask accesses.

Impact: trivial wrap of member accesses

This eases the transition in the next patch.

We also get rid of a temporary cpumask in find_idlest_cpu() thanks to
for_each_cpu_and, and sched_balance_self() due to getting weight before
setting sd to NULL.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -786,6 +786,11 @@ struct sched_group {
 	u32 reciprocal_cpu_power;
 };
 
+static inline struct cpumask *sched_group_cpus(struct sched_group *sg)
+{
+	return &sg->cpumask;
+}
+
 enum sched_domain_level {
 	SD_LV_NONE = 0,
 	SD_LV_SIBLING,
@@ -866,6 +871,11 @@ struct sched_domain {
 #endif
 };
 
+static inline struct cpumask *sched_domain_span(struct sched_domain *sd)
+{
+	return &sd->span;
+}
+
 extern void partition_sched_domains(int ndoms_new, cpumask_t *doms_new,
 				    struct sched_domain_attr *dattr_new);
 extern int arch_reinit_sched_domains(void);