add new hardware
ispprog2: keep ISP_RESET (/SS) as output

ISP_RESET is /SS pin of mega328p.
In master mode, the /SS pin must be configured as output.
If configured as input it must held high to ensure Master SPI operation.
Autodetect SPI frequency

- add statemachine for ISP sync & signature read
- autoprobing of SPI frequency
- remove manual SPI frequency selection
- remove NVM code