Support a runtime configurable T_CHIP_VARIANT

User requested the ability to change chip variant at runtime while maintaining a single class type.

```
typedef DFMiniMp3<HardwareSerial, Mp3Notify, Mp3ChipDynamic> DfMp3; 


Mp3ChipDynamic::setChip(DfMp3_Chip_Original);

or

DfMp3 myMp3();

myMp3.setChip(DfMp3_Chip_Original); // internally calls static Mp3ChipDynamic::setChip

or passed in begin?

```