armv7m: add a TCP channel to stream captured trace

armv7m: add a TCP channel to stream captured trace

When trace capturing the trace is enabled using 'tpiu_config internal'
(via the internal mode), OpenOCD can collect the trace buffers then append
it to a specified file or named pipe and propagate the trace to 'tcl_trace'
command.
This change is allowing OpenOCD to stream the captured trace over TCP.

When using this configuration OpenOCD acts like a server and multiple
clients can connect and receive the captured trace.

Example on STM32F7 running at 216MHz:
  itm port 0 on
  tpiu config internal :3344 uart off 216000000

Change-Id: Idea43e7e26e87b98a33da7fb9acf7ea50fe3b345
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/5345
Tested-by: jenkins
Reviewed-by: Karl Palsson <karlp@tweak.net.au>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>