Add to RF24: Arduino Due supported in SPI_UART

- Add support for Arduino Due secondary SPI BUS using SPI_UART library
(TX1: MOSI, RX1: MISO, SDA1: SCK, CS&CE: User selected)

RF24_config.h

@@ -90,17 +90,19 @@
 
 
  #if defined(__arm__) || defined (__ARDUINO_X86__)
+   #if defined (__arm__) && defined (SPI_UART)
+		#include <SPI_UART.h>
+		#define _SPI uspi
+   #else
      #include <SPI.h>
+     #define _SPI SPI
    #endif
-
- 
- #define _BV(x) (1<<(x))
- #if !defined(__arm__) && !defined (__ARDUINO_X86__)
+ #elif !defined(__arm__) && !defined (__ARDUINO_X86__)
    extern HardwareSPI SPI;
  #endif
  
+ #define _BV(x) (1<<(x))
   
-  #define _SPI SPI
 #endif
 
   #ifdef SERIAL_DEBUG