ARM: dts: msm: add PMK8350 PON_PBS and PON_HLOS devices

Add devices for the PMK8350 PMIC PON_PBS and PON_HLOS peripherals.
These can be used to detect keypresses and to configure the type
of power off to perform (i.e. shutdown vs restart).

Change-Id: I0ba322df9595e609a51da36d2606f8f5eb2b397e