Bluetooth: btusb: add shutdown function for QCA6174

[ Upstream commit 187f8b64 ]

We should send hci reset command before bt turn off, which can reset bt
firmware status.

Signed-off-by: Rocky Liao <quic_rjliao@quicinc.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>