Input: elantech - Prepare a complete software node for the device

Creating a software node and supplying that for the device
instead of only the device properties in it. A software
node was always created in any case to hold the additional
device properties, so this change does not have any real
effect.

This change makes it possible to remove support for the
problematic "dangling" device properties from i2c subsystem,
i.e. the "properties" member from struct i2c_board_info. The
problems caused by them are not related to this driver.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>