mfd: Add MAX8997/8966 IRQ control

This patch enables IRQ handling for MAX8997/8966 chips.

Please note that Fuel-Gauge-related IRQs are not implemented in this
initial release. The fuel gauge module in MAX8997 is identical to
MAX17042, which is already in Linux kernel. In order to use the
already-existing MAX17042 driver for fuel gauge module in MAX8997, the
main interrupt handler of MAX8997 should relay related interrupts to
MAX17042 driver. However, in order to do this, we need to modify
MAX17042 driver as well because MAX17042 driver does not have any
interrupt handlers for now. We are not going to implement this in this
initial release as it is not crucial in basic operations of MAX8997.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>