I know this is an old thread, but I started a project that uses the Driver Board linked above and a 7-inch 800x480 resistive display.
The Adafruit_RA8875 library is working very well for me on a photon. I did have to make one slight modification to the library though. In Adafruit_RA8875.cpp I had to add the following line:
#define SPI_HAS_TRANSACTION 1