mfd: add irq domain support for max8997 interrupts

Add irq domain support for max8997 interrupts. The reverse mapping method
used is linear mapping since the sub-drivers of max8997 such as regulator
and charger drivers can use the max8997 irq_domain to get the linux irq
number for max8997 interrupts. All uses of irq_base in platform data and
max8997 driver private data are removed.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>