tc: support TUI mode for terminals

Once when run in the TMUX session, it launches 4 panes for every
termimal. So we can simply debug the system with the terminal.

Add a new option "--tumx" to allow uses to launch console terminals in
TUI sessions. This option is exclusive with "--telnet" option, only one
of them can be used.

The original idea comes from Qixiang Xu <qixiang.xu@arm.com>.

Suggested-by: Qixiang Xu <qixiang.xu@arm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>