Bluetooth: Use HCI request for LE connection

This patch introduces a new helper, which uses the HCI request
framework, for creating LE connectons. All the handling is now
done by this function so we can remove the hci_cs_le_create_conn()
event handler.

This patch also removes the old hci_le_create_connection() since
it is not used anymore.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>