Bluetooth: Update mgmt powered HCI commands to use async requests

This patch updates sending of HCI commands related to mgmt_set_powered
(e.g. class, name and EIR data) to be sent using asynchronous requests.
This is necessary since it's the only (well, at least the cleanest) way
to keep the power on procedure synchronized and let user space know it
has completed only when all HCI commands are completed (this actual fix
is coming in a subsequent patch).

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>