Input: ALPS - add semi-MT support for v4 protocol

This patch adds semi-MT support for ALPS v4 protocol touchpads.
It is based on the work by Seth Forshee for ALPS v3 and v4 protocol
support. Three packets are required to assemble and process the MT
data. ST events are reported at once to avoid latency. If there
were two contacts or more, report MT data instead of ST events.

Thanks to Seth Forshee for providing most of the code, guidance
and insight for producing this patch.

Signed-off-by: George Pantalos <gpantalos@gmail.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>