dt-bindings: input: add qpnp-power-on bindings

Add device tree bindings for Qualcomm Technologies, Inc. QPNP
Power-on devices.  These are PMIC peripherals which manage PMIC
power on, power off, key presses, and other related activities.

Change-Id: I07ae4e7e4505b8f4973520532106401ca9f76beb