tick/nohz: Only wake up a single target cpu when kicking a task

When adding a tick dependency to a task, its necessary to
wake up the CPU where the task resides to reevaluate tick
dependencies on that CPU.

However the current code wakes up all nohz_full CPUs, which
is unnecessary.

Switch to waking up a single CPU, by using ordering of writes
to task->cpu and task->tick_dep_mask.

[ mingo: Minor readability edit. ]

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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