Bluetooth: bpa10x: Add support for hci_set_fw_info

The Digianswer sniffer devices allow for reading a firmware specific
information string. If it is available, then inform the Bluetooth core
about it via hci_set_fw_info. That exposes it via debugfs like this:

  # cat /sys/kernel/debug/bluetooth/hci0/firmware_info
  SNIF_102,BB930,02/01/18,10:37:56

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