test: disable BIGNUM support on the test ecc_no_bignum component

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/programs/pkey/key_app_writer.c b/programs/pkey/key_app_writer.c
index e8f3e85..179094c 100644
--- a/programs/pkey/key_app_writer.c
+++ b/programs/pkey/key_app_writer.c
@@ -203,7 +203,9 @@
     mbedtls_ctr_drbg_context ctr_drbg;
 
     mbedtls_pk_context key;
+#if defined(MBEDTLS_RSA_C)
     mbedtls_mpi N, P, Q, D, E, DP, DQ, QP;
+#endif /* MBEDTLS_RSA_C */
 
     /*
      * Set to sane values
@@ -225,9 +227,11 @@
     }
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
+#if defined(MBEDTLS_RSA_C)
     mbedtls_mpi_init(&N); mbedtls_mpi_init(&P); mbedtls_mpi_init(&Q);
     mbedtls_mpi_init(&D); mbedtls_mpi_init(&E); mbedtls_mpi_init(&DP);
     mbedtls_mpi_init(&DQ); mbedtls_mpi_init(&QP);
+#endif /* MBEDTLS_RSA_C */
 
     if (argc < 2) {
 usage:
@@ -423,9 +427,11 @@
 #endif
     }
 
+#if defined(MBEDTLS_RSA_C)
     mbedtls_mpi_free(&N); mbedtls_mpi_free(&P); mbedtls_mpi_free(&Q);
     mbedtls_mpi_free(&D); mbedtls_mpi_free(&E); mbedtls_mpi_free(&DP);
     mbedtls_mpi_free(&DQ); mbedtls_mpi_free(&QP);
+#endif /* MBEDTLS_RSA_C */
 
     mbedtls_pk_free(&key);