feat(esp_adc): option to set number of DMA buffers

Add a configuration option to set the number of DMA buffers used by
adc_continuous driver

Author: mcapdeville

components/esp_adc/Kconfig

@@ -92,6 +92,12 @@ menu "ADC and ADC Calibration"
             The SARADC clock frequency will be set to the nearest integer multiple of sample freq.
             The fractional divisor parameters will be calculated at runtime.
 
+    config ADC_CONTINUOUS_NUM_DMA
+        int "Set the number of DMA buffers"
+        default 5
+        help
+            Configure the number of DMA buffers used by adc
+
     config ADC_ENABLE_DEBUG_LOG
         bool "Enable ADC debug log"
         default n

components/esp_adc/adc_continuous.c

@@ -53,7 +53,11 @@ extern portMUX_TYPE rtc_spinlock; //TODO: Will be placed in the appropriate posi
 #define ADC_ENTER_CRITICAL()  portENTER_CRITICAL(&rtc_spinlock)
 #define ADC_EXIT_CRITICAL()  portEXIT_CRITICAL(&rtc_spinlock)
 
+#ifndef CONFIG_ADC_CONTINUOUS_NUM_DMA
 #define INTERNAL_BUF_NUM      5
+#else
+#define INTERNAL_BUF_NUM      CONFIG_ADC_CONTINUOUS_NUM_DMA
+#endif
 
 /*---------------------------------------------------------------
                    ADC Continuous Read Mode (via DMA)