PMU interrupts are used to detect USB Vbus, wall adaptor, accessories
and holdswitch. A thread is needed to poll the PMU throught I2C, ATM
it does nothing but showing the state of the inputs on the HW debug
menu, funcionallity for each individual input will be added in next
patches.
Change-Id: If93bf2044d1052729237a7fd1431c8493e09f1c7