PSA PBKDF2: add config option

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/psa/crypto_config.h b/include/psa/crypto_config.h
index 736d9ab..03aa86c 100644
--- a/include/psa/crypto_config.h
+++ b/include/psa/crypto_config.h
@@ -72,6 +72,9 @@
 #define PSA_WANT_ALG_MD4                        1
 #define PSA_WANT_ALG_MD5                        1
 #define PSA_WANT_ALG_OFB                        1
+/* PBKDF2-HMAC is not yet support via the PSA API in Mbed TLS.
+ * Note: when adding support, also adjust include/mbedtls/config_psa.h */
+//#define PSA_WANT_ALG_PBKDF2_HMAC                1
 #define PSA_WANT_ALG_RIPEMD160                  1
 #define PSA_WANT_ALG_RSA_OAEP                   1
 #define PSA_WANT_ALG_RSA_PKCS1V15_CRYPT         1