Bluetooth: Use async requests internally in hci_req_sync

Bluetooth: Use async requests internally in hci_req_sync

This patch converts the hci_req_sync() procedure to internaly use the
asynchronous HCI requests.

The hci_req_sync mechanism relies on hci_req_complete() calls from
hci_event.c into hci_core.c whenever a HCI command completes. This is
very similar to what asynchronous requests do and makes the conversion
fairly straight forward by converting hci_req_complete into a request
complete callback. By this change hci_req_complete (renamed to
hci_req_sync_complete) becomes private to hci_core.c and all calls to it
can be removed from hci_event.c.

The commands in each hci_req_sync procedure are collected into their own
request by passing the hci_request pointer to the request callback
(instead of the hci_dev pointer). The one slight exception is the HCI
init request which has the special handling of HCI driver specific
initialization commands. These commands are run in their own request
prior to the "main" init request.

One other extra change that this patch must contain is the handling of
spontaneous HCI reset complete events that some controllers exhibit.
These were previously handled in the hci_req_complete function but the
right place for them now becomes the hci_req_cmd_complete function.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>