Fixes for entropy test suite for some configurations

Changes to allow the entropy tests to work for configurations without an
entropy seed file (MBEDTLS_ENTROPY_NV_SEED), and with no entropy sources
configured (MBEDTLS_TEST_NULL_ENTROPY).
diff --git a/tests/suites/test_suite_entropy.data b/tests/suites/test_suite_entropy.data
index 5ca99f8..e0dfae3 100644
--- a/tests/suites/test_suite_entropy.data
+++ b/tests/suites/test_suite_entropy.data
@@ -53,4 +53,9 @@
 entropy_nv_seed:"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
 
 Entropy self test
-entropy_selftest:
+depends_on:!MBEDTLS_TEST_NULL_ENTROPY
+entropy_selftest:0
+
+Entropy self test (MBEDTLS_TEST_NULL_ENTROPY)
+depends_on:MBEDTLS_TEST_NULL_ENTROPY
+entropy_selftest:1
diff --git a/tests/suites/test_suite_entropy.function b/tests/suites/test_suite_entropy.function
index d1ef94b..5b97cad 100644
--- a/tests/suites/test_suite_entropy.function
+++ b/tests/suites/test_suite_entropy.function
@@ -123,7 +123,7 @@
  * END_DEPENDENCIES
  */
 
-/* BEGIN_CASE depends_on:MBEDTLS_FS_IO */
+/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_NV_SEED:MBEDTLS_FS_IO */
 void entropy_seed_file( char *path, int ret )
 {
     mbedtls_entropy_context ctx;
@@ -210,7 +210,7 @@
                  == MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
     TEST_ASSERT( mbedtls_entropy_gather( &ctx )
                  == MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
-#if defined(MBEDTLS_FS_IO)
+#if defined(MBEDTLS_FS_IO) && defined(MBEDTLS_ENTROPY_NV_SEED)
     TEST_ASSERT( mbedtls_entropy_write_seed_file( &ctx, path )
                  == MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
     TEST_ASSERT( mbedtls_entropy_update_seed_file( &ctx, path )
@@ -378,8 +378,8 @@
 /* END_CASE */
 
 /* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
-void entropy_selftest( )
+void entropy_selftest( int result )
 {
-    TEST_ASSERT( mbedtls_entropy_self_test( 0 ) == 0 );
+    TEST_ASSERT( mbedtls_entropy_self_test( 0 ) == result );
 }
 /* END_CASE */