tools: initial version of the SPLL debug trace recorder tool. Currently only the eRTM board is supported

- clean up debug definitions in spll_debug.h
- proper support for AUX channels and events (lock, unlock, gain switch)
- support for up to 8 channels and 16 traces per channel
- optional undersampling for slow readout interfaces (e.g. the UART of the eRTM board)

rename board.h to board-config.h,
remove v1 in Kconfig