x86: Initialize GDT entry 1 to be the 32-bit CS as well

Some OS (like VxWorks) requires GDT entry 1 to be the 32-bit CS.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Jian Luo <jian.luo4@boschrexroth.de>