Bluetooth: Convert hci_req_sync family of function to new request API

Now that there's an API in place that allows passing the resulting skb
to the request callback we can conveniently convert the hci_req_sync and
related functions to use it. Since we still need to get the skb from the
async callback into the sleeping _sync() function the patch adds another
req_skb variable to hci_dev where the sync request state is tracked.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>