first prototype WFM demodulation - kind of working

[DD4WH]

to enable WFM stereo demodulation, alter line 95 in uhsdr_board.c [only possible with DDC RF frontend]

• automatically compiles for 192ksps audio sample rate
• FreeDV is disabled (not enough memory)
• implemented Stereo demodulation on F7
• has to be tested, if possible on F4 --> if not, compile time switches have to be installed
• no switching of demodulation mode yet, only software switch
• still searching for correct gain and phase adjustment values --> empirical research needed
• not yet implemented: 15kHz lowpass & 19kHz notch & de-emphasis