Add Einstart-S support (#11219)

Indeed the HAL does not need to be mucked around with to expose ATmega2560 pins not available as numbers on the MEGA board, I'll need to update the wiki with that tidbit and a reference to the pin-mapping comment in `fastio_1280.h`.

Marlin/src/inc/Conditionals_LCD.h

@@ -201,6 +201,18 @@
   #endif
 #endif
 
+/**
+ * SPI PANELS
+ */
+
+ // Einstart OLED has Cardinal nav via pins defined in pins_EINSTART-S.h
+ #if ENABLED(U8GLIB_SH1106_EINSTART)
+   #define ULTRA_LCD
+   #define DOGLCD
+   #define ULTIPANEL
+   #define NEWPANEL
+ #endif
+
 /**
  * I2C PANELS
  */