arm64: Remove boot thread synchronisation for spin-table release method

The synchronisation with the boot thread already happens in __cpu_up()
via wait_for_completion_timeout(). In addition, __cpu_up() calls are
protected by the cpu_add_remove_lock mutex and already serialised.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 6400111399e16a535231ebd76389c894ea1837ff
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>