Input: elo - add support for non-pressure-sensitive touchscreens

- Use the touch status bit rather than the pressure bits to
  distinguish a BTN_TOUCH event. Non-pressure-sensitive touchscreens
  always report full pressure
- Report ABS_PRESSURE information only if the touchscreen supports it

Signed-off-by: Shaun Jackman <sjackman@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>