Bluetooth: btusb: Add shutdown routine for BTUSB_INTEL_NEW devices

If BT operations (BREDR inquiry/LE scan) were triggered
through the stack, followed by BT turn off through
'hciconfig hci0 down', the controller would still be active
and consume power.
Also, there is a possibility that a race condition/
synchronization issue might arise on the subsequent BT turn
on, as the controller might try to push the
events that were queued up before processing the HCI Reset
command.

btusb_shutdown_intel_new routine shall reset the controller
and stop all BT operation.
Advantages:
	1. Power save on the platform
	2. Host and controller will be in Sync.

Signed-off-by: Raghuram Hegde <raghuram.hegde@intel.com>
Signed-off-by: Chethan T N <chethan.tumkur.narayan@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>