Fix FYSETC S6 I2C EEPROM size (#20340)

Both V1.2 and V2.0 boards have a 24LC16, which is a 2kB EEPROM.

Co-authored-by: PingWin <kirill@shashlov.ru>
Co-authored-by: Jason Smith <jason.inet@gmail.com>

Marlin/src/pins/pins.h

   #include "stm32f4/pins_VAKE403D.h"            // STM32F4
 #elif MB(FYSETC_S6)
   #include "stm32f4/pins_FYSETC_S6.h"           // STM32F4                                env:FYSETC_S6
+#elif MB(FYSETC_S6_V2_0)
+  #include "stm32f4/pins_FYSETC_S6_V2_0.h"      // STM32F4                                env:FYSETC_S6
 #elif MB(FLYF407ZG)
   #include "stm32f4/pins_FLYF407ZG.h"           // STM32F4                                env:FLYF407ZG
 #elif MB(MKS_ROBIN2)
   #include "stm32f4/pins_MKS_ROBIN2.h"          // STM32F4                                env:MKS_ROBIN2
-#elif MB(FYSETC_S6_V2_0)
-  #include "stm32f4/pins_FYSETC_S6_V2_0.h"      // STM32F4                                env:FYSETC_S6
 
 //
 // ARM Cortex M7

Marlin/src/pins/stm32f4/pins_FYSETC_S6.h

 //
 #if NO_EEPROM_SELECTED
   #define FLASH_EEPROM_EMULATION
-  //#define SRAM_EEPROM_EMULATION
   //#define I2C_EEPROM
 #endif
 
   // 128 kB sector allocated for EEPROM emulation.
   #define FLASH_EEPROM_LEVELING
 #elif ENABLED(I2C_EEPROM)
-  #define MARLIN_EEPROM_SIZE              0x1000  // 4KB
+  #define MARLIN_EEPROM_SIZE              0x0800  // 2KB
 #endif
 
 //

Marlin/src/pins/stm32f4/pins_FYSETC_S6_V2_0.h

 #if NO_EEPROM_SELECTED
   #undef NO_EEPROM_SELECTED
   //#define FLASH_EEPROM_EMULATION
-  //#define SRAM_EEPROM_EMULATION
   #define I2C_EEPROM
 #endif