keymap: Lenovo Thinkpad USB Keyboard with Tracepoint

Add support for special function keys on Lenovo Thinkpad USB Keyboard
Tracepoint.

    - VoIP hotkey "FN+F6" is mapped to camera, and may need to change
      if there is a standard VoIP hotkey defined.
    - Mute Microphone key has not been defined, as there is no
      standard key defined for it yet.

Signed-off-by: Jerone Young <jerone.young@canonical.com>
Signed-off-by: Martin Pitt <martin.pitt@ubuntu.com>