Add bignum_new.c starting with MPI_CORE(montmul) for Montgomery multiplication

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index ad0e599..cfa5e46 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -2016,6 +2016,7 @@
  *          library/bignum_core.c
  *          library/bignum_mod.c
  *          library/bignum_mod_raw.c
+ *          library/bignum_new.c
  * Caller:  library/dhm.c
  *          library/ecp.c
  *          library/ecdsa.c