x86: efi-x86_app: Convert to text environment

Use the common include. Drop the unnecessary changes, since missing
stdio drivers will be ignored.

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>