DOGM: Avoid white flash on TFT (re)init (#14631)

- Avoid white flash on TFT (re)init. Unlike Graphical LCD, the TFT init color may be full white if the backlight is on during init.

- Add a conditional for delayed backlight init which can be applied to any backlit display.

Marlin/src/inc/Conditionals_LCD.h

@@ -233,6 +233,7 @@
  #if ENABLED(MKS_ROBIN_TFT)
    #define DOGLCD
    #define IS_ULTIPANEL
+   #define DELAYED_BACKLIGHT_INIT
  #endif
 
 /**

Marlin/src/lcd/dogm/ultralcd_DOGM.cpp

@@ -219,26 +219,34 @@ void MarlinUI::set_font(const MarlinFont font_nr) {
 // Initialize or re-initialize the LCD
 void MarlinUI::init_lcd() {
 
-  #if PIN_EXISTS(LCD_BACKLIGHT) // Enable LCD backlight
+  #if PIN_EXISTS(LCD_BACKLIGHT)
-    OUT_WRITE(LCD_BACKLIGHT_PIN, HIGH);
+    OUT_WRITE(LCD_BACKLIGHT_PIN, (
+      #if ENABLED(DELAYED_BACKLIGHT_INIT)
+        LOW  // Illuminate after reset
+      #else
+        HIGH // Illuminate right away
+      #endif
+    ));
   #endif
 
   #if EITHER(MKS_12864OLED, MKS_12864OLED_SSD1306)
     SET_OUTPUT(LCD_PINS_DC);
-    #if !defined(LCD_RESET_PIN)
+    #ifndef LCD_RESET_PIN
       #define LCD_RESET_PIN LCD_PINS_RS
     #endif
   #endif
 
   #if PIN_EXISTS(LCD_RESET)
-    OUT_WRITE(LCD_RESET_PIN, LOW); // perform a clean hardware reset
+    // Perform a clean hardware reset with needed delays
+    OUT_WRITE(LCD_RESET_PIN, LOW);
+    _delay_ms(5);
+    WRITE(LCD_RESET_PIN, HIGH);
     _delay_ms(5);
-    OUT_WRITE(LCD_RESET_PIN, HIGH);
+    u8g.begin();
-    _delay_ms(5); // delay to allow the display to initialize
   #endif
 
-  #if PIN_EXISTS(LCD_RESET)
+  #if PIN_EXISTS(LCD_BACKLIGHT) && ENABLED(DELAYED_BACKLIGHT_INIT)
-    u8g.begin();
+    WRITE(LCD_BACKLIGHT_PIN, HIGH);
   #endif
 
   #if HAS_LCD_CONTRAST
@@ -246,11 +254,11 @@ void MarlinUI::init_lcd() {
   #endif
 
   #if ENABLED(LCD_SCREEN_ROT_90)
-    u8g.setRot90();   // Rotate screen by 90°
+    u8g.setRot90();
   #elif ENABLED(LCD_SCREEN_ROT_180)
-    u8g.setRot180();  // Rotate screen by 180°
+    u8g.setRot180();
   #elif ENABLED(LCD_SCREEN_ROT_270)
-    u8g.setRot270();  // Rotate screen by 270°
+    u8g.setRot270();
   #endif
 
   uxg_SetUtf8Fonts(g_fontinfo, COUNT(g_fontinfo));