Bluetooth: Add BT_CHANNEL_POLICY socket option

Allow control of AMP functionality on L2CAP sockets. By default,
connections will be restricted to BR/EDR.  Manipulating the
BT_CHANNEL_POLICY option allows for channels to be moved to or created
on AMP controllers.

Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>