tps65912: irq: add interrupt controller

This module controls the interrupt handling for the tps65912.
The interrupt sources can be the following:

- GPIO
- PWRON signal
- PWRHOLD signal
- Temperature detection

Signed-off-by: Margarita Olaya Cabrera <magi@slimlogic.co.uk>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>