treewide: kill global line lookup

treewide: kill global line lookup

Global line lookup doesn't really work correctly because GPIO line names
are not unique. We'd have to return a list of matching lines. Also: not
all chips may be accessible by user in which case the chip iterator will
fail. We'll soon be removing chip iterators entirely so for now drop the
global line lookup and let users iterate over chips themselves.

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