TiLDA_EPD: Clean up all non DUE SPI code, should make it clean for ..

...porting to RTOS later

When I first ported the EPD driver I added a load of if def's to keep non due compatibility

This cleans up all that code thats not need as long as we keep to the Due extended SPI 
http://arduino.cc/en/Reference/DueExtendedSPI