drivers/console: Add a basic telnet console

Telnet is started as an application, as it requires the net stack to be
ready. It will listen to any IP address on both protocols (IPv4, IPv6),
depending of course on which one is enabled.

Current behavior is very basic, as it does not handle any telnet
command (IAC). These will be silently ignored.

Jira: ZEP-1601

Change-Id: Id50656f23e6347bbbc893416953f1ba7116ef87d
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>