mfd: Handle the ab8500 irq for suspend/resume

Ensure that the AB interrupt is only handled at a time when
all core drivers are resumed. Ensure that the AB interrupt
is marked as a wakeup interrupt.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Reviewed-by: Jonas Aberg <jonas.aberg@stericsson.com>
Reviewed-by: Mattias Wallin <mattias.wallin@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>