Bluetooth: Add the cryptographic toolbox function h8

Add to the cryptographic toolbox the h8 function, defined in the Bluetooth
Core Vol. 6, part E 1.1.1.

Also add test and SMP self test for this function. The data used for those
are from the Bluetooth Core.

Signed-off-by: Théo Battrel <theo.battrel@nordicsemi.no>