ctxless: provide new event monitor

ctxless: provide new event monitor

Current implementation of gpiod_ctxless_event_loop() (and its variant
for multiple lines) always requests GPIO lines for listening for both
rising and falling edge events. This causes a problem when the
underlying hardware doesn't allow this.

It can e.g. result in the following error raised by the interrupt
controller:

  genirq: Setting trigger mode 3 for irq 107 failed (kempld_irq_set_type+0x0/0x130 [gpio_kempld])

For the sake of backward compatibility we're leaving the old
implementation in place and provide two new routines that that take an
additional parameter allowing users to specify the events libgpiod
should listen for.

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