Bluetooth: Read adversiting channel TX power during init sequence

This patch adds the reading of the LE advertising channel TX power to
the HCI init sequence of LE-capable controllers. This data will be used
e.g. for inclusion in the advertising data packets when advertising is
enabled.

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>