x86: coreboot: Convert to text environment

Use the common include and add some options specific to this board.

Drop everything from the config.h file.

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/coreboot/coreboot/coreboot.env

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#include <env/x86.env>
+
+splashsource=virtio_fs
+splashimage=0x1000000