Bluetooth: Add skeleton for HCI core

To introduce the Bluetooth stack to the tree we need some additions to
the configuration options, as well as the very basic header files. The
patch also adds a skeleton for a bt_init() function that applications
will need to call to initialize Bluetooth functionality.

Change-Id: Ideb24dfea584b71f514e05eb47654b659776133e
Co-authored-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
8 files changed