Fix Xcelium warnings and errors with simple system

      .test_en_i             ('b0),
                                |
xmelab: *W,CUVMPW (../src/lowrisc_ibex_ibex_simple_system_0/rtl/ibex_simple_system.sv,185|32): port sizes differ in port connection (32/1).
      .debug_req_i           ('b0),
                                |
xmelab: *W,CUVMPW (../src/lowrisc_ibex_ibex_simple_system_0/rtl/ibex_simple_system.sv,214|32): port sizes differ in port connection (32/1).
      .fetch_enable_i        ('b1),
                                |
xmelab: *W,CUVMPW (../src/lowrisc_ibex_ibex_simple_system_0/rtl/ibex_simple_system.sv,216|32): port sizes differ in port connection (32/1).
  always_ff @(posedge clk_i or negedge rst_ni) begin
          |
xmelab: *E,MULAXX (../src/lowrisc_ibex_sim_shared_0/rtl/sim/simulator_ctrl.sv,59|10): Multiple drivers to always_ff output variable sim_finish detected.
  always_ff @(posedge clk_i or negedge rst_ni) begin
          |
xmelab: *E,MULAXX (../src/lowrisc_ibex_sim_shared_0/rtl/sim/simulator_ctrl.sv,59|10): Multiple drivers to always_ff output variable sim_finish detected.
  always_ff @(posedge clk_i or negedge rst_ni) begin
          |
xmelab: *E,MULAXX (../src/lowrisc_ibex_sim_shared_0/rtl/sim/simulator_ctrl.sv,59|10): Multiple drivers to always_ff output variable sim_finish detected.
xrun: *E,ELBERR: Error during elaboration (status 1), exiting.

Start by reproducing the Xcelium elaboration errors in the simple-system setup. Inspect src/lowrisc_ibex_ibex_simple_system_0/rtl/ibex_simple_system.sv at the reported port connections and src/lowrisc_ibex_sim_shared_0/rtl/sim/simulator_ctrl.sv around line 59. Done means the reported port-size warnings and multiple-driver errors no longer occur during elaboration.