Better ST7920 timings for FYSETC S6 (#16022)

Marlin/src/pins/stm32/pins_FYSETC_S6.h

 #if HAS_TMC220x
   /**
    * TMC2208/TMC2209 stepper drivers
-   *
    */
 
   //
 
 // Alter timing for graphical display
 #if HAS_GRAPHICAL_LCD
-  #define BOARD_ST7920_DELAY_1 DELAY_NS(96)
-  #define BOARD_ST7920_DELAY_2 DELAY_NS(48)
-  #define BOARD_ST7920_DELAY_3 DELAY_NS(600)
+  #ifndef BOARD_ST7920_DELAY_1
+    #define BOARD_ST7920_DELAY_1 DELAY_NS(103)
+  #endif
+  #ifndef BOARD_ST7920_DELAY_2
+    #define BOARD_ST7920_DELAY_2 DELAY_NS(51)
+  #endif
+  #ifndef BOARD_ST7920_DELAY_3
+    #define BOARD_ST7920_DELAY_3 DELAY_NS(642)
+  #endif
 #endif
 
 #ifndef RGB_LED_R_PIN
 #ifndef RGB_LED_W_PIN
   #define RGB_LED_W_PIN    -1
 #endif
-