Input: wistron_btns - simplify dependencies

Kconfig symbol X86_32 was introduced in October 2005, it's about time
to use it. This clears the last occurrence of the legacy
"X86 && !X86_64" construct :-)

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>