[SAMD51] Activate ADCs oversampled 12bits (#15874)

Marlin/src/HAL/HAL_SAMD51/HAL.cpp

       // Preloaded data (fixed for all ADC instances hence not loaded by DMA)
       adc->REFCTRL.bit.REFSEL = ADC_REFCTRL_REFSEL_AREFA_Val;               // VRefA pin
       SYNC(adc->SYNCBUSY.bit.REFCTRL);
-      adc->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_10BIT_Val;
+      adc->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_12BIT_Val;
       SYNC(adc->SYNCBUSY.bit.CTRLB);
       adc->SAMPCTRL.bit.SAMPLEN = (6 - 1);                                  // Sampling clocks
+      adc->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM_16 | ADC_AVGCTRL_ADJRES(4);  // 16 Accumulated conversions and shift 4 to get oversampled 12 bits result
+      SYNC(adc->SYNCBUSY.bit.AVGCTRL);
       // Registers loaded by DMA
       adc->DSEQCTRL.bit.INPUTCTRL = true;
 

Marlin/src/HAL/HAL_SAMD51/HAL.h

 
 void HAL_adc_init();
 
+#define HAL_ADC_FILTERED            // Disable oversampling done in Marlin as ADC values already filtered in HAL
+#define HAL_ADC_RESOLUTION  12
 #define HAL_START_ADC(pin)  HAL_adc_start_conversion(pin)
-#define HAL_ADC_RESOLUTION  10
 #define HAL_READ_ADC()      HAL_adc_result
 #define HAL_ADC_READY()     true