x86: theadorable-x86-xxx_defconfig: Enable setexpr command

The setexpr command is useful for scripting, lets enable it for all
x86 based theadorable platforms.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>