atmel_maxtouch: Set input property bit to indicate a direct input device

Prop bit is checked in userspace and must be set in
driver in order to be recognized correctly, since it defaults
to mouse pointer.

Change-Id: I8432716573a365c11b6837d1ce756364d2b98946
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>