irqchip/armada-370-xp: Make syscore_ops static

irqchip/armada-370-xp: Make syscore_ops static

The armada_370_xp_mpic_syscore_ops structure is not exported or
declared anywhere. Fix the following warning by making it static:

drivers/irqchip/irq-armada-370-xp.c:544:20: warning: symbol 'armada_370_xp_mpic_syscore_ops' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://lkml.kernel.org/r/1465408533-13906-1-git-send-email-ben.dooks@codethink.co.uk
Signed-off-by: Jason Cooper <jason@lakedaemon.net>