Configs: Enable PSA key derivation in Profile Small

It is more resaonable to execute the whole TLS-PSK key derivation
inside SPE. Enable PSA key derivation interface in Profile Small.
Update the design document accordingly.

Change-Id: Ie84dce2f70dbf538661528f877762400ba98d651
Signed-off-by: David Hu <david.hu@arm.com>
3 files changed