Compile fix: smp_send_pull_timers() depends on CONFIG_SMP

Add defined(CONFIG_SMP) in kernel/hrtimer.c.
Compile fix: include litmus/litmus.h in kernel/sched/core.c

Sometimes the header is included incirectly, but not always.
Compile fix: rq->cpu depends on CONFIG_SMP

Fix this dependency in kernel/sched/core.c.
Compile fix: rq->cpu depends on CONFIG_SMP

Fix this dependency in kernel/sched/litmus.c.
Compile fix: use DECLARE_PER_CPU_SHARED_ALIGNED in header

Under some configurations, using extern
DEFINE_PER_CPU_SHARED_ALIGNED() causes link failures.
Compile fix: include litmus/litmus.h in kernel/mutex.c

Reported by Hiroyuki Chishiro <chishiro@cs.unc.edu> and
Daniel Bristot de Oliveira <danielbristot@gmail.com>.