Fix dsim support

[akashlevy]

This PR fixes up Ibex UVM support for dsim simulator. Several things had to be fixed:

• Simulator compatibility: dsim requires that enum values must use enum constants
  • Use ZERO enum value instead of '0 and 0 for instr enums
  • Protect Ibex-specific CSRs with `ifndef DSIM to ensure these are not included in implemented_csr[]. dsim requires that all array values be enumerated in privileged_reg_t, which they are currently not
• Simulator compatibility: dsim does not appear to respect "re-exports"
  • Replace all re-exported ibex_mem_intf_agent_pkg::ADDR_WIDTH and ibex_mem_intf_agent_pkg::DATA_WIDTH with ibex_mem_intf_pkg::ADDR_WIDTH and ibex_mem_intf_pkg::DATA_WIDTH
• Script fix: Add dsim case for reloc_word in dv/uvm/core_ibex/scripts/run_instr_gen.py
• Script fix: Remove extra quote in dv/uvm/core_ibex/yaml/rtl_simulation.yaml
• Script fix: Replace dsim_compile_opts with dsim_opts in util/ibex_config.py

With these fixes, I was able to get all the UVM tests passing with SIMULATOR=dsim.