ALL: Massive 'const' cleanup

These changes facilitate more robust parameter type checking and helps
to identify unexpected coding errors.

Most simulators can now also be compiled with a C++ compiler without
warnings.

Additionally, these changes have also been configured to facilitate easier
backporting of simulator and device simulation modules to run under the
simh v3.9+ SCP framework.

SDS/sds_drm.c

@@ -105,7 +105,6 @@ int32 drm_ftime = 3;                                    /* time to fetch */
 int32 drm_xtime = 1;                                    /* time to xfr */
 int32 drm_stopioe = 1;                                  /* stop on error */
 
-DEVICE drm_dev;
 t_stat drm (uint32 fnc, uint32 inst, uint32 *dat);
 t_stat drm_svc (UNIT *uptr);
 t_stat drm_reset (DEVICE *dptr);