core: add non-closing gpiochip iterator function and foreach macro

core: add non-closing gpiochip iterator function and foreach macro

Allows users to iterate over the gpiochips without closing them
automatically. The lines can then be used during the runtime of the
program. The user is responsible for closing the chips after they are
no longer needed.

Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>