Input: add support for Elan eKTF2127 touchscreen controller

This adds a driver for the Elan eKTF2127 touchscreen controller,
which speaks an i2c protocol which is distinctly different from
the already supported eKTH controllers.

Signed-off-by: Michel Verlaan <michel.verl@gmail.com>
Signed-off-by: Siebren Vroegindeweij <siebren.vroegindeweij@hotmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>