Bluetooth: hci_uart: Add protocol support for Broadcom UART devices

This adds the protocol support for Broadcom based UART devices to
enable firmware and patchram download procedure. It is a pretty
straight forward H:4 driver with the exception of actually having
its own setup and address configuration callbacks.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>