Bluetooth: Add dedicated AES instance for each SMP context

Many places have to be extra careful to not hold the hdev lock when
calling into the SMP code. This is because the SMP crypto functions use
the crypto handle that's part of the hci_dev struct. Giving the SMP
context its own handle helps simplifying the locking logic and removes
the risk for deadlocks.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>