efi_selftest: export efi_st_get_config_table()

We can use efi_st_get_config_table() in multiple unit tests.
Export the function.

Export system-table and boot-services.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_selftest/efi_selftest_util.c b/lib/efi_selftest/efi_selftest_util.c
index dba02d6..7e03e0c 100644
--- a/lib/efi_selftest/efi_selftest_util.c
+++ b/lib/efi_selftest/efi_selftest_util.c
@@ -110,3 +110,14 @@
 	}
 	return 0;
 }
+
+void *efi_st_get_config_table(const efi_guid_t *guid)
+{
+	size_t i;
+
+	for (i = 0; i < st_systable->nr_tables; i++) {
+		if (!guidcmp(guid, &st_systable->tables[i].guid))
+			return st_systable->tables[i].table;
+	}
+	return NULL;
+}