Bluetooth: btusb: Release RF resource on BT shutdown

Issue description: Intel 7265 shares the same RF with Wifi and BT.
In the shutdown scenario turn off BT, followed by turn WiFi off
and on causing error in RF calibration in WiFi Module

Solution: before shutdown BT ensure any RF activity to clear by
HCI reset command.

Reference Logs:
ERR kernel: [ 386.193284] iwlwifi 0000:01:00.0: Failed to run INIT calibrations: -5
ERR kernel: [ 386.193298] iwlwifi 0000:01:00.0: Failed to run INIT ucode: -5
ERR kernel: [ 386.193309] iwlwifi 0000:01:00.0: Failed to start RT ucode: -5

Signed-off-by: Amit K Bag <amit.k.bag@intel.com>
Singed-off-by: Chethan T N <chethan.tumkur.narayan@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>