Apply #pragma once, misc cleanup (#12322)

* Apply #pragma once in headers
* Adjust some thermistors formatting
* Misc cleanup and formatting

Marlin/src/HAL/HAL_DUE/HAL.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * Description: HAL for Arduino Due and compatible (SAM3X8E)
@@ -26,9 +27,6 @@
  * For ARDUINO_ARCH_SAM
  */
 
-#ifndef _HAL_DUE_H
-#define _HAL_DUE_H
-
 #define CPU_32_BIT
 
 #include <stdint.h>
@@ -189,5 +187,3 @@ char *dtostrf (double __val, signed char __width, unsigned char __prec, char *__
 #ifdef __cplusplus
   }
 #endif
-
-#endif // _HAL_DUE_H