x86: slimbootloader: Convert to text environment

Use the common include along with some additions.

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>
[Drop common env from slimbootloader.env]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

board/intel/slimbootloader/slimbootloader.env

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2019 Intel Corporation <www.intel.com>
+ */
+
+#include <env/x86.env>
+
+/* don't use video */
+stdout=serial
+stderr=serial
+
+usb_pgood_delay=40
+
+ramdiskaddr=0x4000000
+ramdiskfile=initrd
+bootdev=usb
+bootdevnum=0
+bootdevpart=0
+bootfsload=fatload
+bootusb=setenv bootdev usb; boot
+bootscsi=setenv bootdev scsi; boot
+bootmmc=setenv bootdev mmc; boot
+bootargs=console=ttyS0,115200 console=tty0