Target independent protocol implementation for serial DPM handling

Currently the serial DPM examples are existing multiple times for different host targets. And the implementation of the SPI protocol and the SPI read/write functions for the specific netX chips are packed togther in one big source module.

This could be done in a more modular way, by separating the serial DPM protocol from the chip specific SPI interface to become more usable for customers and eaysier to adapt to customer specific host systems.