powerpc: Fix a lazy irq related WARING in arch_local_irq_restore()

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: Li Zhong <zhong@linux.vnet.ibm.com>
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Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>