When applying touchscreen parameters specified in device tree let's make
sure we keep whatever setup was done by the driver and not reset the
missing values to zero.
Reported-by: NPavel Machek <pavel@ucw.cz>
Tested-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

Add common DT binding documentation for touchscreen devices and
implement input_parse_touchscreen_of_params, which parses the common
properties and configures the input device accordingly.

The method currently does not interpret the axis inversion properties,
since there is no matching flag in the generic linux input device.
Reviewed-by: NPavel Machek <pavel@ucw.cz>
Acked-by: NAaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: NSebastian Reichel <sre@kernel.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>