The pseries CPU hotplug code uses cede_processor without properly
synchronizing the SW and HW interrupt enable state. This fixes
it using the same helpers that were written for the idle code.
Signed-off-by: NLi Zhong <zhong@linux.vnet.ibm.com>

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Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>