Bluetooth: Add support for SMP phase 3 (key distribution)

This adds support for generating and distributing all the keys
specified in the third phase of SMP.

This will make possible to re-establish secure connections, resolve
private addresses and sign commands.

For now, the values generated are random.

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