Input: atmel_mxt_ts - report pressure information from the driver

Atmel mxt1386 touch controller has the touch pressure information so
let's report it to the user space.

[dtor@mail.ru: added ABS_RESSURE reporting for ST emulation.]

Signed-off-by: Yufeng Shen <miletus@chromium.org>
Acked-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>