core: remove kernel data structures from struct gpiod_line
core: remove kernel data structures from struct gpiod_line

The structures defined in linux/gpio.h use non-standard data types.

Use them only when calling relevant ioctl()s and then copy the
necessary info to separate fields in struct gpiod_line.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod