input: Add new sun4i-ts driver for Allwinner sunxi SoC's rtp controller

Note the sun4i-ts controller is capable of detecting a second touch, but when
a second touch is present then the accuracy becomes so bad the reported touch
location is not useable.

The original android driver contains some complicated heuristics using the
aprox. distance between the 2 touches to see if the user is making a pinch
open / close movement, and then reports emulated multi-touch events around
the last touch coordinate (as the dual-touch coordinates are worthless).

These kinds of heuristics are just asking for trouble (and don't belong
in the kernel). So this driver offers straight forward, reliable single
touch functionality only.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
ARM: dts: sun7i: Add rtp controller node

Signed-off-by: Hans de Goede <hdegoede@redhat.com>