pk: add alternate function for keypair generation using PSA

Instead of using the legacy mbedtls_ecp_gen_keypair() which makes
use of ECP's math, when USE_PSA_CRYPTO is enabled then the new
function pk_genkey_ec() is used in test_suite_pk.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index b6144d9..d09b5f5 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -1214,6 +1214,7 @@
  * \return          An \c MBEDTLS_ERR_ECP_XXX or \c MBEDTLS_MPI_XXX error code
  *                  on failure.
  */
+#if !defined(MBEDTLS_USE_PSA_CRYPTO)
 int mbedtls_ecp_gen_keypair(mbedtls_ecp_group *grp, mbedtls_mpi *d,
                             mbedtls_ecp_point *Q,
                             int (*f_rng)(void *, unsigned char *, size_t),
@@ -1235,6 +1236,7 @@
 int mbedtls_ecp_gen_key(mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,
                         int (*f_rng)(void *, unsigned char *, size_t),
                         void *p_rng);
+#endif /* !MBEDTLS_USE_PSA_CRYPTO */
 
 /**
  * \brief           This function reads an elliptic curve private key.