Input: ili210x - rework the touchscreen sample processing

Get rid of the packed structures for representing data as that does not
apply to other similar Ilitek touchscreens. Instead, implement a function
which parses the data and reports touch events and coordinates.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>