Switch SD2cadrLib to fastio

Replace all fastDigitalRead/Write() with READ/WRITE()

Define SCK_PIN, MISO_PIN, MOSI_PIN in pins.h if not already defined in the pins_*.h files.

Remove these conditional pin definitions from the pin-files. They are now always defined.

Define separate sets of SPI-pins for AT90USB with and without Teensy support in fastio.h.
Likely this was the main reason for all that confusion about the AT90USB-SPI pins.

Marlin/pins.h

@@ -432,4 +432,19 @@
     X_MS1_PIN, X_MS2_PIN, Y_MS1_PIN, Y_MS2_PIN, Z_MS1_PIN, Z_MS2_PIN \
   }
 
+#define HAS_DIGIPOTSS (PIN_EXISTS(DIGIPOTSS))
+
+#ifndef SCK_PIN
+  #define SCK_PIN  SCK
+#endif
+#ifndef MISO_PIN
+  #define MISO_PIN MISO
+#endif
+#ifndef MOSI_PIN
+  #define MOSI_PIN MOSI
+#endif
+#ifndef SS_PIN
+  #define SS_PIN   SS
+#endif
+
 #endif //__PINS_H