tools: gpio: add multi-line monitoring to gpio-event-mon

tools: gpio: add multi-line monitoring to gpio-event-mon

Extend gpio-event-mon to support monitoring multiple lines.
This would require multiple lineevent requests to implement using uAPI v1,
but can be performed with a single line request using uAPI v2.

Signed-off-by: Kent Gibson <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Bartosz Golaszewski <[email protected]>