drivers/console/telnet: Add ground support for telnet commands

This is the skeleton for such support. Let's see if this will be needed
and thus extended in the future.

For now, it's disabled by default, not advised to be enabled.
It supports AYT, AO and DO/SUPR_GA. This is very limited and only there
to show how it could be handled.

Change-Id: I736bfa23145e9b727af08db682ab001f494f8c8d
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>