Allow MAX31865 resistance values configuration (#19695)

Marlin/Configuration.h

@@ -432,6 +432,12 @@
 #define DUMMY_THERMISTOR_998_VALUE 25
 #define DUMMY_THERMISTOR_999_VALUE 100
 
+// Resistor values when using a MAX31865 (sensor -5)
+// Sensor value is typically 100 (PT100) or 1000 (PT1000)
+// Calibration value is typically 430 ohm for AdaFruit PT100 modules and 4300 ohm for AdaFruit PT1000 modules.
+//#define MAX31865_SENSOR_OHMS      100
+//#define MAX31865_CALIBRATION_OHMS 430
+
 // Use temp sensor 1 as a redundant sensor with sensor 0. If the readings
 // from the two sensors differ too much the print will be aborted.
 //#define TEMP_SENSOR_1_AS_REDUNDANT

Marlin/src/inc/SanityCheck.h

@@ -1845,6 +1845,10 @@ static_assert(hbm[Z_AXIS] >= 0, "HOMING_BUMP_MM.Z must be greater than or equal
   #error "TEMP_SENSOR_1 is required with TEMP_SENSOR_1_AS_REDUNDANT."
 #endif
 
+#if ENABLED(MAX6675_IS_MAX31865) && (!defined(MAX31865_SENSOR_OHMS) || !defined(MAX31865_CALIBRATION_OHMS))
+  #error "MAX31865_SENSOR_OHMS and MAX31865_CALIBRATION_OHMS must be set in Configuration.h when using a MAX31865 temperature sensor."
+#endif
+
 /**
  * Test Heater, Temp Sensor, and Extruder Pins
  */

Marlin/src/module/temperature.cpp

@@ -1461,7 +1461,7 @@ void Temperature::manage_heater() {
         #elif ENABLED(HEATER_0_USES_MAX6675)
           return (
             #if ENABLED(MAX6675_IS_MAX31865)
-              max31865.temperature(100, 400)  // 100 ohms = PT100 resistance. 400 ohms = calibration resistor
+              max31865.temperature(MAX31865_SENSOR_OHMS, MAX31865_CALIBRATION_OHMS)
             #else
               raw * 0.25
             #endif
@@ -2236,7 +2236,7 @@ void Temperature::disable_all_heaters() {
     next_max6675_ms[hindex] = ms + MAX6675_HEAT_INTERVAL;
 
     #if ENABLED(MAX6675_IS_MAX31865)
-      max6675_temp = int(max31865.temperature(100, 400)); // 100 ohms = PT100 resistance. 400 ohms = calibration resistor
+      max6675_temp = int(max31865.temperature(MAX31865_SENSOR_OHMS, MAX31865_CALIBRATION_OHMS));
     #endif
 
     //