Input: edt-ft5x06 - add support for Evervision FT5726

Evervision displays are using different Focaltech touchscreen
controllers. This commit adds the initial support for the ones using the
FT5726 controller. Receiving the touch data is the same as for the
GENERIC_FT but the x and y cooridnates are swapped. The main differences
are the register addresses where the GAIN and THRESHOLD parameters are
stored.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>