Apply #pragma once, misc cleanup (#12322)

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

Marlin/src/HAL/HAL_AVR/fastio_644.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * Pin mapping for the 644, 644p, 644pa, and 1284p
@@ -53,9 +54,6 @@
  *                        +--------+
  */
 
-#ifndef _FASTIO_644_H_
-#define _FASTIO_644_H_
-
 #include "fastio_AVR.h"
 
 #define DEBUG_LED   DIO0
@@ -552,5 +550,3 @@
 #define PD7_WPORT   PORTD
 #define PD7_DDR     DDRD
 #define PD7_PWM     OCR2A
-
-#endif // _FASTIO_644_H_