Bluetooth: btusb: Support public address configuration for MediaTek Chip.

The MediaTek chip support vendor specific HCI command(0xfc1a) to
change the public address. Add hdev->set_bdaddr handler for MediaTek
Chip. After doing a power cycle or MediaTek Bluetooth reset, BD_ADDR
will bring back the original one.

Signed-off-by: mark-yw.chen <mark-yw.chen@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>