x86: edison: Convert to text environment

Don't use the common include since Edison's environment is empty.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> # Intel Edison
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

board/intel/edison/edison.env

@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2017 Intel Corp.
+ */
+
+/* empty environment */