event: rework gpiod_line_event_wait_bulk()

event: rework gpiod_line_event_wait_bulk()

When monitoring more than one line, it's possible for two or more
events to be queued at the same time in the kernel, so the internal
call to ppoll() will return a value greater than 1. If we always only
read one event at most, we end up calling ppoll() needlessly, as we
already know more events are pending.

Allow gpiod_line_event_wait_bulk() to pass a list of all lines on
which events occurred via a line bulk object.

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