Ok, so that Cypress part will make it easier, but still not "easy". First, you're going to need to understand the Cypress chip's function (I don't have time for that). Once you understand that, you're going to have to implement a UART in your FPGA. You will have to configure the Cypress part. The "easy" part is simply writing data to your UART on one board and reading data from the UART on the other board. It looks like this could be interrupt driven, if that's necessary.
Is it necessary to use USB? There's an RS-232 port available which would be MUCH easier to implement. What is your speed requirement?