Recover 32 bytes of SRAM in Marlin bootscreen code

Marlin/ultralcd_impl_HD44780.h

   }
 
   void bootscreen() {
-    byte top_left[8] = {
+    const static PROGMEM byte corner[4][8] = { {
       B00000,
       B00000,
       B00000,
       B00010,
       B00100,
       B00100
-    };
-    byte top_right[8] = {
+    }, {
       B00000,
       B00000,
       B00000,
       B01100,
       B00100,
       B00100
-    };
-    byte botom_left[8] = {
+    }, {
       B00100,
       B00010,
       B00001,
       B00000,
       B00000,
       B00000
-    };
-    byte botom_right[8] = {
+    }, {
       B00100,
       B01000,
       B10000,
       B00000,
       B00000,
       B00000
-    };
-    lcd.createChar(0, top_left);
-    lcd.createChar(1, top_right);
-    lcd.createChar(2, botom_left);
-    lcd.createChar(3, botom_right);
+    } };
+    for (uint8_t i = 0; i < 4; i++)
+      createChar_P(i, corner[i]);
 
     lcd.clear();