Input: ALPS - add interleaved protocol support (Dell E6x00 series)

Properly handle version of the protocol where standard PS/2 packets
from trackpoint are stuffed into middle (byte 3-6) of the standard
ALPS packets when both the touchpad and trackpoint are used together.

The patch is based on work done by Matthew Chapman and additional
research done by David Kubicek and Erik Osterholm:

	https://bugs.launchpad.net/ubuntu/+source/linux/+bug/296610

Many thanks to David Kubicek for his efforts in researching fine points
of this new version of the protocol, especially interaction between pad
and stick in these models.

Signed-off-by: Sebastian Kapfer <sebastian_kapfer@gmx.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>