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_timers_Due.h

@@ -18,6 +18,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * HAL for Arduino Due and compatible (SAM3X8E)
@@ -25,9 +26,6 @@
  * For ARDUINO_ARCH_SAM
  */
 
-#ifndef _HAL_TIMERS_DUE_H
-#define _HAL_TIMERS_DUE_H
-
 // --------------------------------------------------------------------------
 // Includes
 // --------------------------------------------------------------------------
@@ -120,5 +118,3 @@ FORCE_INLINE static void HAL_timer_isr_prologue(const uint8_t timer_num) {
 }
 
 #define HAL_timer_isr_epilogue(TIMER_NUM)
-
-#endif // _HAL_TIMERS_DUE_H