Fix MAX6675 SPI init, conflicts (#20086)

Marlin/src/MarlinCore.cpp

 
   SETUP_RUN(HAL_init());
 
+  // Init and disable SPI thermocouples
+  #if HEATER_0_USES_MAX6675
+    OUT_WRITE(MAX6675_SS_PIN, HIGH);  // Disable
+  #endif
+  #if HEATER_1_USES_MAX6675
+    OUT_WRITE(MAX6675_SS2_PIN, HIGH); // Disable
+  #endif
+
   #if HAS_L64XX
     SETUP_RUN(L64xxManager.init());  // Set up SPI, init drivers
   #endif

Marlin/src/module/temperature.cpp

     INIT_FAN_PIN(CONTROLLER_FAN_PIN);
   #endif
 
-  #if MAX6675_SEPARATE_SPI
-
-    OUT_WRITE(SCK_PIN, LOW);
-    OUT_WRITE(MOSI_PIN, HIGH);
-    SET_INPUT_PULLUP(MISO_PIN);
-
-    max6675_spi.init();
-
-    OUT_WRITE(SS_PIN, HIGH);
-    OUT_WRITE(MAX6675_SS_PIN, HIGH);
-
-  #endif
-
-  #if HEATER_1_USES_MAX6675
-    OUT_WRITE(MAX6675_SS2_PIN, HIGH);
-  #endif
+  TERN_(MAX6675_SEPARATE_SPI, max6675_spi.init());
 
   HAL_adc_init();
 
       spiInit(MAX6675_SPEED_BITS);
     #endif
 
-    MAX6675_SET_OUTPUT();
     MAX6675_WRITE(LOW);  // enable TT_MAX6675
-
     DELAY_NS(100);       // Ensure 100ns delay
 
     // Read a big-endian temperature value