core: kill gpiod_line_get()

core: kill gpiod_line_get()

We're dropping all interfaces for global line lookup and accessing. Lines
should be always accessed via their owning chip object.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>