This patch adds irq domain support for max8998 interrupts.

To keep both non-DT and DT worlds happy, simple domain is used, which is
linear when no explicit IRQ base is specified and legacy, with static
mapping, otherwise.
Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>