sched/smp: Always define sched_domains_mutex_lock()/unlock(), def_root_domain and sched_domains_mutex

Simplify the scheduler by making CONFIG_SMP=y primitives and data
structures unconditional.

Unconditionally build kernel/sched/topology.c and the main sched-domains
locking primitives.

Signed-off-by: Ingo Molnar <[e-mail]>
Acked-by: Peter Zijlstra <[e-mail]>
Cc: Dietmar Eggemann <[e-mail]>
Cc: Juri Lelli <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: Shrikanth Hegde <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Valentin Schneider <[e-mail]>
Cc: Vincent Guittot <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

include/linux/sched.h

···
 	UCLAMP_CNT
 };
 
-#ifdef CONFIG_SMP
 extern struct root_domain def_root_domain;
 extern struct mutex sched_domains_mutex;
 extern void sched_domains_mutex_lock(void);
 extern void sched_domains_mutex_unlock(void);
-#else
-static inline void sched_domains_mutex_lock(void) { }
-static inline void sched_domains_mutex_unlock(void) { }
-#endif
 
 struct sched_param {
 	int sched_priority;

kernel/sched/build_utility.c

···
 #ifdef CONFIG_SMP
 # include "cpupri.c"
 # include "stop_task.c"
-# include "topology.c"
 #endif
+
+#include "topology.c"
 
 #ifdef CONFIG_SCHED_CORE
 # include "core_sched.c"

kernel/sched/topology.c

···
 	mutex_unlock(&sched_domains_mutex);
 }
 
+#ifdef CONFIG_SMP
+
 /* Protected by sched_domains_mutex: */
 static cpumask_var_t sched_domains_tmpmask;
 static cpumask_var_t sched_domains_tmpmask2;
···
 	partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
 	sched_domains_mutex_unlock();
 }
+
+#endif /* CONFIG_SMP */