Use MD-light in entropy.c

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/build_info.h b/include/mbedtls/build_info.h
index e66032d..949b115 100644
--- a/include/mbedtls/build_info.h
+++ b/include/mbedtls/build_info.h
@@ -99,6 +99,7 @@
  */
 #if defined(MBEDTLS_ECJPAKE_C) || \
     defined(MBEDTLS_PEM_PARSE_C) || \
+    defined(MBEDTLS_ENTROPY_C) || \
     defined(MBEDTLS_PKCS12_C) || \
     defined(MBEDTLS_RSA_C)
 #define MBEDTLS_MD_LIGHT