timers: Avoid blocking on hrtimer_cpu_base lock during Oops or panic

sysrq_timer_list_show()改用NMI安全的ktime_get_mono_fast_ns()，print_active_timers()在Oops/panic/NMI下用raw_spin_trylock_irqsave()，失败即记录竞争并返回，避免hrtimer锁或timekeeping seq死等。