Handle dependency on ECP_C in ECC KDF

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 31da1b4..bc19ed0 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -5559,6 +5559,7 @@
     uint8_t **data
     )
 {
+#if defined(MBEDTLS_ECP_C)
     unsigned key_out_of_range = 1;
     mbedtls_mpi k;
     mbedtls_mpi diff_N_2;
@@ -5642,6 +5643,13 @@
     mbedtls_mpi_free(&k);
     mbedtls_mpi_free(&diff_N_2);
     return status;
+#else /* MBEDTLS_ECP_C */
+    (void) slot;
+    (void) bits;
+    (void) operation;
+    (void) data;
+    return PSA_ERROR_NOT_SUPPORTED;
+#endif /* MBEDTLS_ECP_C */
 }
 
 /* ECC keys on a Montgomery elliptic curve draws a byte string whose length