Bluetooth: hci_qca: Fix qca6390 enable failure after warm reboot

Warm reboot can not reset controller qca6390 due to
lack of controllable power supply, so causes firmware
download failure during enable.

Fixed by sending VSC EDL_SOC_RESET to reset qca6390
within added device shutdown implementation.

Signed-off-by: Zijun Hu <zijuhu@codeaurora.org>
Tested-by: Zijun Hu <zijuhu@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>