🐛 Fix dual MAX31865 initialization issues (#23496)

Marlin/src/libs/MAX31865.h

@@ -101,11 +101,7 @@ private:
 
   TERN(LARGE_PINMAP, uint32_t, uint8_t) sclkPin, misoPin, mosiPin, cselPin;
 
-  #ifdef TARGET_LPC1768
-    uint8_t spiSpeed;
-  #else
-    uint16_t spiDelay;
-  #endif
+  uint16_t spiDelay;
 
   float zeroRes, refRes, wireRes;
 
@@ -121,6 +117,11 @@ private:
     one_shot_event_t nextEvent;
   #endif
 
+  #ifdef MAX31865_IGNORE_INITIAL_FAULTY_READS
+    uint8_t ignore_faults = MAX31865_IGNORE_INITIAL_FAULTY_READS;
+    uint16_t fixFault(uint16_t rtd);
+  #endif
+
   uint8_t stdFlags = 0;
 
   void setConfig(uint8_t config, bool enable);
@@ -130,9 +131,12 @@ private:
   uint16_t readRegister16(uint8_t addr);
 
   void writeRegister8(uint8_t addr, uint8_t reg);
-  uint8_t spiTransfer(uint8_t addr);
+  void writeRegister16(uint8_t addr, uint16_t reg);
 
-  void softSpiBegin(const uint8_t spi_speed);
+  void softSpiInit();
+  void spiBeginTransaction();
+  uint8_t spiTransfer(uint8_t addr);
+  void spiEndTransaction();
 
   void initFixedFlags(max31865_numwires_t wires);
 
@@ -141,6 +145,10 @@ private:
   void oneShot();
   void resetFlags();
 
+  uint16_t readRawImmediate();
+
+  void runAutoFaultDetectionCycle();
+
 public:
   #if ENABLED(LARGE_PINMAP)
     MAX31865(uint32_t spi_cs, uint8_t pin_mapping);