Persistent storage common code from
test_suite_psa_crypto_slot_management.function had been duplicated in
test_suite_psa_crypto_se_driver_hal.function and the copy had slightly
diverged. Re-align the copy in preparation from moving the code to a
common module and using that sole copy in both test suites.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>