[nrf fromlist] tests: secure_storage: its: enable PSA Crypto core w/ custom transform

Enable the Mbed TLS PSA Crypto core also in the custom ITS transform
implementation case so that CONFIG_SECURE_STORAGE is able to select
CONFIG_MBEDTLS_PSA_CRYPTO_STORAGE_C.

Signed-off-by: Tomi Fontanilles <[email protected]>

Upstream PR #: 85735

(cherry picked from commit fdea391d1bad3a1f0265ba45a6fe1f90bab039cf)
Signed-off-by: Tomi Fontanilles <[email protected]>

Author: tomi-font

tests/subsys/secure_storage/psa/its/overlay-transform_custom.conf

@@ -2,3 +2,8 @@ CONFIG_SECURE_STORAGE_ITS_TRANSFORM_IMPLEMENTATION_CUSTOM=y
 CONFIG_SECURE_STORAGE_ITS_TRANSFORM_OUTPUT_OVERHEAD=0
 
 CONFIG_SECURE_STORAGE_ITS_MAX_DATA_SIZE=500
+
+# Enable the Mbed TLS PSA Crypto core even though it's not needed directly;
+# it's for CONFIG_MBEDTLS_PSA_CRYPTO_STORAGE_C to be selectable.
+CONFIG_MBEDTLS=y
+CONFIG_MBEDTLS_PSA_CRYPTO_C=y