evdev: move device opening out from evdev_input_device_create

evdev: move device opening out from evdev_input_device_create

This makes the generic evdev code (i.e. the functions not relying on
udev) independent of launcher-util too. The aim is to allow re-using the
generic evdev code in the Android backend, where neither udev nor
launcher-util are available.

evdev_input_device_create() signature is changed:
- add the opened device file descriptor
- remove wl_display as unused

Also add a bit of failure logging.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>