M5StickC Plus 2: Power.isCharging() not working

[jsoeterbroek]

For M5StickC Plus 2 the function Power.isCharging() is not working (returning charge_unknown).
In Power_Class.cpp there is a missing case statement for pmic_t::pmic_adc

[Tinyu-Zhao]

The CHRG pin of the TP4057 is not connected to any I/O, so its status should not be readable.