Bluetooth: Move power on HCI command updates to their own function

These commands will in a subsequent patch be performed in their own
asynchronous request, so it's more readable (not just from a resulting
code perspective but also the way the patches look like) to have them
performed in their own 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>