Add SYSINFO flag to check if processor is being simulated

[stnolting]

This PR adds a new flag to the SYSINFO module to check if the processor is being simulated:
NEORV32_SYSINFO.SOC bit 13: SYSINFO_SOC_IS_SIM, set if processor is being simulated

The state of this flag cannot be guaranteed for all platforms as it depends on the toolchains 'pragma' support (works with GHDL, Intel Quartus, Lattice Radiant):

  -- Check if we're inside the Matrix -------------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  constant is_simulation_c : boolean := false -- seems like we're on real hardware
-- pragma translate_off
-- synthesis translate_off
-- synthesis synthesis_off
-- RTL_SYNTHESIS OFF
  or true -- this MIGHT be a simulation
-- RTL_SYNTHESIS ON
-- synthesis synthesis_on
-- synthesis translate_on
-- pragma translate_on
  ;