stack: remove acquire fence on push
stack: remove acquire fence on push

An acquire fence is used to make sure loads after the fence can observe
all store operations before a specific store-release.
But push doesn't read any data, except for the head which is part of a
CAS operation (the items on the list are not read).
So there is no need for the acquire barrier.

Signed-off-by: Steven Lariau <e2599038859a9d62e62b7ae81de43bd9ecf09397@arm.com>
Reviewed-by: Dharmik Thakkar <724f3610823e4b14afc73144686337ac966281c2@arm.com>
Reviewed-by: Ruifeng Wang <a548d51fbc42485a8ba807711a537e88c2b59dd2@arm.com>
Acked-by: Gage Eads <40e74f4682b7928915cbf15b25c304eff85f59a4@intel.com>

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