input: touchscreen: Add support for Atmel Maxtouch

Atmel Maxtouch is a multi-touch controller chip series
which supports ATMXT224 and ATMXT1386.

Change-Id: I26a054732df37c171dcb5547edfbe4913e494b30
Signed-off-by: Iiro Valkonen <iiro.valkonen@atmel.com>
[Kconfig and Makefile changes by amaloche@codeaurora.org]
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>