With the removal of old tpiu code, commit 7e6556b3ca ("server:
permit the add_service function to return the created service")
http://openocd.zylin.com/5717/ can be reverted.

Fix also the new calls to add_service().

Change-Id: Ib7f2dfc6a9e829239e20313e0f121911085fdc00
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6031
Tested-by: jenkins
Reviewed-by: Adrian M Negreanu <adrian.negreanu@nxp.com>

Real Time Transfer (RTT) is an interface specified by SEGGER based on
basic memory reads and writes to transfer data bidirectionally between
target and host.
Every target that supports so called "background memory access", which
means that the target memory can be accessed by the debugger while the
target is running, can be used.

RTT is especially of interest for targets which do not support Serial
Wire Output (SWO) (e.g. ARM Cortex-M0) or where using semihosting is
not possible (e.g. real-time applications) [1].

The data transfer is organized in channels where each channel consists
of an up- and/or down-channel. See [2] for more details.

Channels are exposed via TCP connections. One or more RTT server can be
assigned to each channel to make them accessible to an unlimited number
of TCP connections.

The current implementation does not respect buffer flags which are used
to determine what happens when writing to a full buffer.

Note that the implementation is designed in a way that the RTT
operations can be directly performed by an adapter (e.g. J-Link).

[1] https://devzone.nordicsemi.com/tutorials/6/
[2] https://www.segger.com/jlink-rtt.html

Change-Id: I8bc8a1b381fb74e08b8752d5cf53804cc573c1e0
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: http://openocd.zylin.com/4055
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>