Bluetooth: Add support for reading LE supported states

The LE supported states indicate the states and state combinations that
the link layer supports. This is important information for knowing what
operations are possible when dealing with multiple connected devices.
This patch adds reading of the supported states to the HCI init
sequence.

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>