In the UVM registers chapter description, the path to the spi package has been provided which implements the uvm ral.
I have downloaded that package and found that ral model for the spi dut has been generated automatically. The file shows the below :
// THIS IS AUTOMATICALLY GENERATED CODE
// Generated by Mentor Graphics' Register Assistant V3.0.0 Engineering Build
// UVM Register Kit version 1.0
I am using the questa sim tool but unable to locate the register assistant.