mfd: wcd9xxx: Introduce wcd9xxx interrupt controller driver

The wcd9xxx codec hardwares have multiple interrupt sources that share
one phycial interrupt line which is usually a gpio.
Convert the current wcd9xxx interrupt controller implementation to a driver
that registers itself to irq domain so codec drivers can utilize
interrupts without worrying about gpio source and system interrupt number.

Change-Id: I35381b90f0db49dbdcd70811d4adc16e40dd7ba2
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>