tools: gpio: remove the include directory on make clean

Remove the generated include directory when running make clean.

Fixes: 8674cea8 ("tools/gpio: move to tools buildsystem")
Signed-off-by: Zhang Jiao <zhangjiao2@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20250903063621.2424-1-zhangjiao2@cmss.chinamobile.com


[Bartosz: add Fixes tag, improve the commit message]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>