input: add features mechanism

input: add features mechanism

This commit discards the simplistic udev check for the ID_KEYBOARD
property in favor of a more direct "feature" probing. This is done for
the following reasons:

- We will need to use input devices which are not necessarily keyboards,
  for example the PC speaker to sound the bell.

- To differentiate between keyboard with certain capabilities, such as
  LEDs (indicators). We can then perform actions on devices according to
  their feature bits.

- We check directly for what we need, i.e. the ability to send/receive
  certain evdev events, without relying on logic in udev. This also
  reduces our dependency on udev if we ever want to make it optional.

Signed-off-by: Ran Benita <ran234@gmail.com>
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>