Apply #pragma once, misc cleanup (#12322)

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

Marlin/src/HAL/HAL_AVR/ServoTimers.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * ServoTimers.h - Interrupt driven Servo library for Arduino using 16 bit timers- Version 2
@@ -39,9 +40,6 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#ifndef _SERVOTIMERS_H_
-#define _SERVOTIMERS_H_
-
 /**
  * Defines for 16 bit timers used with  Servo library
  *
@@ -91,5 +89,3 @@ typedef enum {
   #endif
   _Nbr_16timers
 } timer16_Sequence_t;
-
-#endif // _SERVOTIMERS_H_