WIP: Bluetooth: Add le_auto_conn file on debugfs

This patch adds to debugfs the le_auto_conn file. Reading this file
we get a list a all auto connect devices. The file format is the
following:
<address> <address type> <auto_connect>

Writting on this file will add a new address to LE auto connect
list.

This file is created only if LE is enabled.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>