Allow use of either SD Card slot when LCD Panel is configured.

Preference is for Controller SD slot before LCD Panel slot when both are occupied.

Marlin/cardreader.cpp

   if(root.isOpen())
     root.close();
 #ifdef SDSLOW
-  if (!card.init(SPI_HALF_SPEED,SDSS))
+  if (!card.init(SPI_HALF_SPEED,SDSS)
+  #if defined(LCD_SDSS) && (LCD_SDSS != SDSS)
+    && !card.init(SPI_HALF_SPEED,LCD_SDSS)
+  #endif
+    )
 #else
-  if (!card.init(SPI_FULL_SPEED,SDSS))
+  if (!card.init(SPI_FULL_SPEED,SDSS)
+  #if defined(LCD_SDSS) && (LCD_SDSS != SDSS)
+    && !card.init(SPI_FULL_SPEED,LCD_SDSS)
+  #endif
+    )
 #endif
   {
     //if (!card.init(SPI_HALF_SPEED,SDSS))

Marlin/pins.h

         #define BTN_EN1 47  //reverse if the encoder turns the wrong way.
         #define BTN_EN2 43
         #define BTN_ENC 32
-        #define SDSS 53
+        #define LCD_SDSS 53
         #define SDCARDDETECT -1
         #define KILL_PIN 41
       #elif defined(LCD_I2C_VIKI)
         #define BTN_EN1 22  //reverse if the encoder turns the wrong way.
         #define BTN_EN2 7
         #define BTN_ENC -1
-        #define SDSS 53
+        #define LCD_SDSS 53
         #define SDCARDDETECT 49
       #else
         //arduino pin which triggers an piezzo beeper
      #ifdef LCD_I2C_PANELOLU2
        #ifdef MELZI
          #define BTN_ENC 29 //the click switch
-         #define SDSS 30 //to use the SD card reader on the Panelolu2 rather than the melzi board
+         #define LCD_SDSS 30 //to use the SD card reader on the Panelolu2 rather than the melzi board
        #else
          #define BTN_ENC 30 //the click switch
        #endif