cpu/hotplug: Rework callback invocation logic

This is preparation for the following patch.
This rework here changes the arguments of cpuhp_invoke_callback(). It
passes now `state' and whether `startup' or `teardown' callback should
be invoked. The callback then is looked up by the function.

The following is a clanup of callers:
- cpuhp_issue_call() has one argument less
- struct cpuhp_cpu_state (which is used by the hotplug thread) gets also
  its callback removed. The decision if it is a single callback
  invocation moved to the `single' variable. Also a `bringup' variable
  has been added to distinguish between startup and teardown callback.
- take_cpu_down() needs to start one step earlier. We always get here
  via CPUHP_TEARDOWN_CPU callback. Before that change cpuhp_ap_states +
  CPUHP_TEARDOWN_CPU pointed to an empty entry because TEARDOWN is saved
  in bp_states for this reason. Now that we use cpuhp_get_step() to
  lookup the state we must explicitly skip it in order not to invoke it
  twice.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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