Bluetooth: Add special handling with __hci_request and HCI_INIT

To support a more dynamic HCI initialization sequence the __hci_request
behavior requires some more changes. Particularly, the init sequence
should be able to have conditionals in it (sending some HCI commands
depending on the outcome of a previous command) instead of being a fixed
list as it is right now.

The reasons for these additional requirements are the moving all
previously user space driven initialization commands to the kernel side
as well as the support the Low Energy controllers.

To fulfull these requirements the init sequence is made the only special
case for multi-command requests and req_last_cmd is renamed to
init_last_cmd. The hci_send_cmd function is changed to update
init_last_cmd as long as the HCI_INIT flag is set.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>