Add calibration of DAC values to be programmed to smooth/flatten the
distribution. This gets rid of the range jumps when transistors are
switched/added and uses the old psi46v2 lookup table from the ATB firmware.
This is applied to all DACs, since 8bit DACs behave the same and 4bit
DACs are not affected. This behaviour can be disabled using
FLAG_DISABLE_DACCAL.
Firmware version now at 2.4