Fixed True SPI for Arduino Due

[RykilthKnox]

Added a definition for the SPI frequency of the arduino due

• I have added a macro definition for the sam3x8e chip (Arduino Due) in the frequency and another macro definition of the constructor of true SPI

• The frequency value i used in the definition is highest frequency that i was able to test stably with my one (and only) Arduino Due. I have also tested it with a custom board board that uses the same sam3x8e chip. I have also added a true SPI constructor definition for the sam3x8e chip that is identical to the ESP8266. This addition is an improvement to the default constructor and improves the "tft.fillRect(0, 0, 128, 128, BLACK);" by 1ms

• True SPI with the given example "test.ino" does not work. After adding the definition it should function normonally on the Arduino Due and board that uses the sam3x8e chip

[ladyada]

@makermelissa looks good to me, but take a look too :) no need to test, we dont technically support Due