host side for barebox remote control ...

This contains the host tool for barebox remote control. It is written in
Phython with its own implementation of the RATP protocol. Currently this
is a very simple tool which needs more work, but the code can also be
used as a library.

Example output:

console: '.      '
console: '..     '
console: 'dev    '
console: 'env    '
console: 'mnt    '
console: '\n'
Result: BBPacketCommandReturn(exit_code=0)

Signed-off-by: Jan Lübbe <j.luebbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Tested-by: Andrey Smirnov <andrew.smirnov@gmail.com>