Fix build TEST_NS_PS without TEST_S_PS.

PS Test partition is build only if TEST_S_PS is ON while there is no
need in PS Test partition for non-secure protected storage tests. This
patch enable PS Test partition only if TEST_S_PS is ON.

Signed-off-by: Bohdan Hunko <Bohdan.Hunko@infineon.com>
Change-Id: Id65ffdf152cf31a7c84f10ca3ccf4b5b639b0df0