I have no experience with graphic LCD, but a few thoughts:
1) can you connect a logic analyzer?
2) do you use LCD reset signal? If not, try to control reset line as indicated by datasheet
3) the datasheet you provided also mentions driver IC ST7789, did you use the corresponding datasheet as well? Maybe you'll find adaptable example source code on the web
I see that you have clock set to 12MHz, please increase the clock frequency based on your interface as mentioned below and let me know if it works:
For more info on this please refer to Page 12 of the following document: http://www.cypress.com/file/440296/download