19256: pkg/tinyusb: add GD32VF103 support r=gschorcht a=gschorcht
### Contribution description
This PR provides the tinyUSB support for GD32VF103 and enables the `tinyusb_device` feature as well as `stdio_tinyusb_cdc_acm` for GD32VF103 boards.
### Testing procedure
```
BOARD=sipeeed-longan-nano make -C tests/shell flash term
```
should work
### Issues/PRs references
Co-authored-by: Gunar Schorcht <gunar@schorcht.net>
The ADC configuration was too complex. It was hard to follow when certain ADC lines are available. Furthermore, the order of ADC lines did depend on the use of other peripherals. Now, either the TFT display is not connected and all ADC lines are available or the TFT display is connected and the second SPI device is used so that only the first 4 ADC lines are available.
