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_168.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * Pin mapping for the 168, 328, and 328P
@@ -27,9 +28,6 @@
  *   Port:        B0 B1 B2 B3 B4 B5 C0 C1 C2 C3 C4 C5 C6 C7 D0 D1 D2 D3 D4 D5 D6 D7
  */
 
-#ifndef _FASTIO_168_H_
-#define _FASTIO_168_H_
-
 #include "fastio_AVR.h"
 
 #define DEBUG_LED   AIO5
@@ -357,5 +355,3 @@
 #define PD7_WPORT   PORTD
 #define PD7_DDR     DDRD
 #define PD7_PWM     NULL
-
-#endif // _FASTIO_168_H_