Bluetooth: Move SMP fields to a separate structure

The objective is to make the core to have as little as possible
information about SMP procedures and logic. Now, all the SMP
specific information is hidden from the core.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>