SCP: Add "HELP DEVICE devnam"

This allows for device help to be displayed for devices which may have
names that are ambiguous with respect to commands.  For example
if a device named CON exists, HELP CON will display info about the
CONTINUE command rather than the device.  HELP DEVICE CON will
now display that device's HELP info.

scp.c

@@ -3285,6 +3285,8 @@ if (*cptr) {
         UNIT *uptr;
         t_stat r;
 
+        if (0 == strcmp (gbuf, "DEVICE"))
+            cptr = get_glyph (cptr, gbuf, 0);
         dptr = find_unit (gbuf, &uptr);
         if (dptr == NULL) {
             dptr = find_dev (gbuf);