Input: alps - report pressure of v3 and v7 trackstick

ALPS v3 and v7 packet formats reports trackstick pressure. This information
is already parsed in unused "z" variable.

ALPS SS4 S2 devices already reports trackstick pressure as ABS_PRESSURE
attribute, therefore reports pressure in the same way also for v3 and v7.

This patch also updates parsing v3 pressure information, it is also stored
in 7 bits.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>