rtos: rework rtos_create()

To simplify the caller of rtos_create(), convert the code from
jimtcl oriented to OpenOCD commands.

While there, fix inconsistencies in almost every rtos create()
method and reset rtos_auto_detect to better cooperate on run-time
rtos configuration.

Change-Id: I59c443aaed77a48174facdfc86db75d6b28c8480
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8830
Tested-by: jenkins

src/rtos/ecos.c

@@ -1213,12 +1213,12 @@ static int ecos_create(struct target *target)
 				target->rtos->gdb_thread_packet = ecos_packet_hook;
 				/* We do not currently use the target->rtos->gdb_target_for_threadid
 				 * hook. */
-				return 0;
+				return ERROR_OK;
 			}
 			tnames++;
 		}
 	}
 
 	LOG_ERROR("Could not find target in eCos compatibility list");
-	return -1;
+	return ERROR_FAIL;
 }