Power monitor and display (#17437)

Marlin/src/HAL/LPC1768/HAL.h

@@ -150,6 +150,8 @@ int freeMemory();
                                     // K = 6, 565 samples, 500Hz sample rate, 1.13s convergence on full range step
                                     // Memory usage per ADC channel (bytes): 4 (32 Bytes for 8 channels)
 
+#define HAL_ADC_VREF            3.3 // ADC voltage reference
+
 #define HAL_ADC_RESOLUTION     12   // 15 bit maximum, raw temperature is stored as int16_t
 #define HAL_ADC_FILTERED            // Disable oversampling done in Marlin as ADC values already filtered in HAL