Apply #pragma once, misc cleanup (#12322)

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

Marlin/src/HAL/HAL_AVR/watchdog_AVR.h

@@ -19,9 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-
-#ifndef _WATCHDOG_AVR_H_
-#define _WATCHDOG_AVR_H_
+#pragma once
 
 #include <avr/wdt.h>
 
@@ -31,5 +29,3 @@ void watchdog_init();
 // Reset watchdog. MUST be called at least every 4 seconds after the
 // first watchdog_init or AVR will go into emergency procedures.
 inline void watchdog_reset() { wdt_reset(); }
-
-#endif // _WATCHDOG_AVR_H_