Bluetooth: hci_uart: Add Intel/AG6xx support

This driver implements support for iBT2.1 Bluetooth controller embedded
in the AG620 communication combo. The controller needs to be configured
with bddata and can be patched with a binary patch file (pbn).
These operations are performed in manufacturing mode.

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