Avoid allocating unneeded DMA channels

Audio.h

 #endif
 
 #include "DMAChannel.h"
-#ifndef DMACHANNEL_HAS_BEGIN
+#if !defined(DMACHANNEL_HAS_BEGIN) || !defined(DMACHANNEL_HAS_BOOLEAN_CTOR)
 #error "You need to update DMAChannel.h & DMAChannel.cpp"
 #error "https://github.com/PaulStoffregen/cores/blob/master/teensy3/DMAChannel.h"
 #error "https://github.com/PaulStoffregen/cores/blob/master/teensy3/DMAChannel.cpp"

examples/HardwareTesting/PassThroughMono/PassThroughMono.ino

   // Do nothing here.  The Audio flows automatically
 
   // When AudioInputAnalog is running, analogRead() must NOT be used.
-  delay(200);
-  Serial.print("PDB: SC=");
-  Serial.print(PDB0_SC, HEX);
-  Serial.print(", CONFIG=");
-  Serial.print(PDB_CONFIG, HEX);
-  Serial.print(", MOD=");
-  Serial.print(PDB0_MOD);
-  Serial.print(", IDLY=");
-  Serial.print(PDB0_IDLY);
-  Serial.print(", CH0C1=");
-  Serial.print(PDB0_CH0C1);
-  Serial.print(", DMA: ");
-  Serial.print(dma_channel_allocated_mask, HEX);
-  Serial.println();
 }
 
 

input_adc.cpp

 audio_block_t * AudioInputAnalog::block_left = NULL;
 uint16_t AudioInputAnalog::block_offset = 0;
 bool AudioInputAnalog::update_responsibility = false;
-DMAChannel AudioInputAnalog::dma;
+DMAChannel AudioInputAnalog::dma(false);
 
 
 AudioInputAnalog::AudioInputAnalog() : AudioStream(0, NULL)

input_i2s.cpp

 audio_block_t * AudioInputI2S::block_right = NULL;
 uint16_t AudioInputI2S::block_offset = 0;
 bool AudioInputI2S::update_responsibility = false;
-DMAChannel AudioInputI2S::dma;
+DMAChannel AudioInputI2S::dma(false);
 
 
 void AudioInputI2S::begin(void)

output_dac.cpp

 audio_block_t * AudioOutputAnalog::block_left_1st = NULL;
 audio_block_t * AudioOutputAnalog::block_left_2nd = NULL;
 bool AudioOutputAnalog::update_responsibility = false;
-DMAChannel AudioOutputAnalog::dma;
+DMAChannel AudioOutputAnalog::dma(false);
 
 void AudioOutputAnalog::begin(void)
 {

output_i2s.cpp

 uint16_t  AudioOutputI2S::block_right_offset = 0;
 bool AudioOutputI2S::update_responsibility = false;
 DMAMEM static uint32_t i2s_tx_buffer[AUDIO_BLOCK_SAMPLES];
-DMAChannel AudioOutputI2S::dma;
+DMAChannel AudioOutputI2S::dma(false);
 
 void AudioOutputI2S::begin(void)
 {

output_pwm.cpp

 uint8_t AudioOutputPWM::interrupt_count = 0;
 
 DMAMEM uint32_t pwm_dma_buffer[AUDIO_BLOCK_SAMPLES*2];
-DMAChannel AudioOutputPWM::dma;
+DMAChannel AudioOutputPWM::dma(false);
 
 // TODO: this code assumes F_BUS is 48 MHz.
 // supporting other speeds is not easy, but should be done someday