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/lcd/thermistornames.h

@@ -94,6 +94,8 @@
   #define THERMISTOR_NAME "PT100 4K7"
 #elif THERMISTOR_ID == 110
   #define THERMISTOR_NAME "PT100 1K"
+#elif THERMISTOR_ID == 666
+  #define THERMISTOR_NAME "Einstart S"
 
 // High Temperature thermistors
 #elif THERMISTOR_ID == 66

Marlin/src/lcd/ultralcd_impl_DOGM.h

@@ -181,6 +181,9 @@
   // The MINIPanel display
     //U8GLIB_MINI12864 u8g(DOGLCD_CS, DOGLCD_A0);  // 8 stripes
     U8GLIB_MINI12864_2X u8g(DOGLCD_CS, DOGLCD_A0); // 4 stripes
+#elif ENABLED(U8GLIB_SH1106_EINSTART)
+  // Connected via motherboard header
+  U8GLIB_SH1106_128X64 u8g(DOGLCD_SCK, DOGLCD_MOSI, DOGLCD_CS, LCD_PINS_DC, LCD_PINS_RS);    
 #else
   // for regular DOGM128 display with HW-SPI
     //U8GLIB_DOGM128 u8g(DOGLCD_CS, DOGLCD_A0);  // HW-SPI Com: CS, A0  // 8 stripes