Begin implementing PMU, now successfully read and write registers, need
to implement button functionality, battery voltage readout, charge
detection etc.
TG-553
Zephyr already provides button support based on gpios. We are mapping
Zephyr keycodes to OpenRTX therefore future targets will only need to
configure their devicetrees to have button support.
Rotary encoder readout leverages the hardware pulse counter. PTT in
this device is also bound to KEY_ESC, that matched the behaviour
observed in many commercial radios.
TG-553