Hi,
an internet search "xilinx SPI VHDL" or "xilinx SPI Verilog" gives more than enough hits.
Read through some of them to find out what´s suitable for your application. (we can no know this).
In your next post please give informatrions about your application (wiring, SPI clock frequency, programming language....)
And refer to the document you think that is suitable for your design.
A link to to the ADC datasheet is usefull, too. Then we don´t need to do an internet search.
Klaus