Show bootscreen later

Init display and show bootscreen later, but init display in `kill()`
to init outputs before the bootscreen delays but being able to display
kill errors.

Marlin/ultralcd.h

@@ -52,8 +52,11 @@
   #if ENABLED(DOGLCD)
     extern int lcd_contrast;
     void set_lcd_contrast(int value);
+  #elif ENABLED(SHOW_BOOTSCREEN)
+    void bootscreen();
   #endif
 
+
   #define LCD_MESSAGEPGM(x) lcd_setstatuspgm(PSTR(x))
   #define LCD_ALERTMESSAGEPGM(x) lcd_setalertstatuspgm(PSTR(x))