Bluetooth: Split HCI init sequence into three stages

Having conditional command sending during a request has always been
problematic and caused hacks like the hdev->init_last_cmd variable. This
patch removes these conditionals and instead splits the init sequence
into three stages, each with its own __hci_req_sync() call.

This also paves the way to the upcoming asynchronous request support
swhich will also benefit by having a simpler implementation if it
doesn't need to cater for requests that change on the fly.

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>