mfd: Use genirq in 88pm860x

Use genirq to simplify IRQ handling in 88pm860x. Remove the interface of
mask/free IRQs on 88pm860x. All these work is taken by genirq. Update the
touchscreen driver of 88pm860x since IRQ handling is changed.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>