powerpc/85xx: fix timebase sync issue when CONFIG_HOTPLUG_CPU=n

powerpc/85xx: fix timebase sync issue when CONFIG_HOTPLUG_CPU=n

When CONFIG_SMP=y, timebase synchronization is required when the second
kernel is started.

arch/powerpc/kernel/smp.c:
  int __cpu_up(unsigned int cpu, struct task_struct *tidle)
  {
  	...
  	if (smp_ops->give_timebase)
  		smp_ops->give_timebase();
  	...
  }

  void start_secondary(void *unused)
  {
  	...
  	if (smp_ops->take_timebase)
  		smp_ops->take_timebase();
  	...
  }

When CONFIG_HOTPLUG_CPU=n and CONFIG_KEXEC_CORE=n,
 smp_85xx_ops.give_timebase is NULL,
 smp_85xx_ops.take_timebase is NULL,
As a result, the timebase is not synchronized.

Timebase  synchronization does not depend on CONFIG_HOTPLUG_CPU.

Fixes: 56f1ba280719 ("powerpc/mpc85xx: refactor the PM operations")
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210929033646.39630-3-nixiaoming@huawei.com