removed 'route(..)' due not easily supportable atm. Updated
'dap_enable(..)' in lieu of route. Fixed dap_audio_eq_band(..) bad use
of unsigned. Changed 'updateCoefs(..)' so default behavior is not reset
other three elements of state.

added AudioBiquadFilter::
public:
void updateCoefs(int *source, bool noReset);
void updateCoefs(int *source);

added AudioControlSGTL5000::
private:
unsigned int modify(unsigned int reg, unsigned int val, unsigned int
iMask);

public:
unsigned int micGain(unsigned int n) { return modify(0x002A, n&3, 3); }
unsigned short lo_lvl_right(uint8_t n);
unsigned short lo_lvl_left(uint8_t n);
unsigned short lo_lvl(uint8_t n);
unsigned short dac_vol_right(float n);
unsigned short dac_vol_left(float n);
unsigned short dac_vol(float n);
unsigned short dap_mix_enable(uint8_t n);
unsigned short dap_enable(uint8_t n);
unsigned short dap_peqs(uint8_t n);
unsigned short dap_audio_eq(uint8_t n);
unsigned short dap_audio_eq_band(uint8_t bandNum, float n);
void dap_audio_eq_geq(float bass, float mid_bass, float midrange, float
mid_treble, float treble);
void dap_audio_eq_tone(float bass, float treble);
void load_peq(uint8_t filterNum, int *filterParameters);
void route(uint8_t via_i2s, uint8_t via_dap);