gpio: xtensa: depend on HAVE_XTENSA_GPIO32

Prevent build failure when the selected variant does not support GPIO32.

Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>