Applying updates for Libero SoC support

[CLappin]

This pull request fixes some of the minor issues spotted while evaluating Litex for Libero SoC 2023.02.0.8. Assumption made is that Libero SoC is installed as described Libero_Installation_Licensing_Setup_User_Guide

Also add a tcl command to export the *.job file for FPExpress.

Basic test ran against the FPGA_101 - Lab001 available here Note: only base.py has been updated, need to update load.py still.