Make bootscreen configurable for the graphic displays

Saves about 473 byte of progmem and 28 bytes of RAM.

Marlin/Marlin_main.cpp

@@ -666,7 +666,6 @@ void setup() {
   Config_RetrieveSettings();
 
   lcd_init();
-  _delay_ms(1000);  // wait 1sec to display the splash screen
 
   tp_init();    // Initialize temperature loop
   plan_init();  // Initialize planner;

Marlin/dogm_bitmaps.h

@@ -3,6 +3,7 @@
 // Please note that using the high-res version takes 402Bytes of PROGMEM. 
 //#define START_BMPHIGH
 
+#if ENABLED(SHOW_BOOTSCREEN)
   #if ENABLED(START_BMPHIGH)
     #define START_BMPWIDTH      112
     #define START_BMPHEIGHT      38
@@ -75,6 +76,7 @@
       ,0x60,0x00,0x00,0x00,0x00,0x00,0x06
       ,0x1f,0xff,0xff,0xff,0xff,0xff,0xf8 };
   #endif
+#endif
 
 // Here comes a compile-time operation to match the extruder symbols 
 // on the info screen to the set number of extruders in configuration.h

Marlin/dogm_lcd_implementation.h

@@ -190,7 +190,9 @@ char lcd_printPGM(const char* str) {
   return n;
 }
 
-static bool show_splashscreen = true;
+#if ENABLED(SHOW_BOOTSCREEN)
+  static bool show_bootscreen = true;
+#endif
 
 /* Warning: This function is called from interrupt context */
 static void lcd_implementation_init() {
@@ -220,7 +222,7 @@ static void lcd_implementation_init() {
     u8g.setRot270();  // Rotate screen by 270°
   #endif
 
-  // Show splashscreen
+  #if ENABLED(SHOW_BOOTSCREEN)
     int offx = (u8g.getWidth() - START_BMPWIDTH) / 2;
     #if ENABLED(START_BMPHIGH)
       int offy = 0;
@@ -232,7 +234,7 @@ static void lcd_implementation_init() {
 
     u8g.firstPage();
     do {
-    if (show_splashscreen) {
+      if (show_bootscreen) {
         u8g.drawBitmapP(offx, offy, START_BMPBYTEWIDTH, START_BMPHEIGHT, start_bmp);
         lcd_setFont(FONT_MENU);
         #ifndef STRING_SPLASH_LINE2
@@ -244,7 +246,12 @@ static void lcd_implementation_init() {
         #endif
       }
     } while (u8g.nextPage());
-  show_splashscreen = false;
+
+    if (show_bootscreen) {
+      delay(1000);
+      show_bootscreen = false;
+    }
+  #endif
 }
 
 static void lcd_implementation_clear() { } // Automatically cleared by Picture Loop