Input: atmel_mxt_ts - report pressure information from the driver

Atmel mxt1386 touch controller has the touch pressure information but
the current driver atmel_mxt_ts does not expose it to the user space.
This patch makes the driver report the touch pressure information to
user space.

ChangeLog:
v2: fixed indentation as commented by Wanlong Gao
v3: added signed-off-by

Change-Id: Ib30cca618d964793e026a675823d9ed8d4e912b9
Signed-off-by: Yufeng Shen <miletus@chromium.org>
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>