Bluetooth: hci_uart: Add basic support for Intel Lightning Peak devices

The Intel Lightning Peak devices do not come with Bluetooth firmware
loaded and thus require a full download of the operational Bluetooth
firmware when the device is attached via the Bluetooth line discipline.

Lightning Peak devices start with a bootloader mode that only accepts
a very limited set of HCI commands. The supported commands are enough
to identify the hardware and select the right firmware to load.

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>