Input: Support in the elantech driver of the trackpoint present on for instance Lenovo L530

The Lenovo L530 trackpoint does not work out of the box. It gives sync errors
as shown below when the trackpoint or trackpoint mouse buttons are pressed and
no input is received by userspace:
[   29.010641] psmouse serio1: Touchpad at isa0060/serio1/input0 lost sync at byte 6
The touchpad does work.

The alternative is to do a downgrade to generic ps/2 mouse (modprobe psmouse proto=bare)
but this has the disadvantage that touchpad can't be disabled (I want trackpoint, not touchpad).

With this patch, the trackpoint is provided as another input device; currently called 'TPPS/2 IBM TrackPoint'
The trackpoint now succesfully works and I can disable the touchpad with synclient TouchPadOff=1
The patch will also output messages that do not follow the expected pattern.
In the mean time I've seen 2 unknown packets occasionally:
0x04 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00
0x00 , 0x00 , 0x00 , 0x02 , 0x00 , 0x00
I don't know what those are for, but they can be safely ignored.

Currently all packets that are not known to v3 touchpad and where packet[3] (the fourth byte) lowest
nibble is 6 are now recognized as PACKET_TRACKPOINT and processed by the new elantech_report_trackpoint.

This has been verified to work on a laptop where the touchpad/trackpoint combined identify themselves as:
psmouse serio1: elantech: assuming hardware version 3 (with firmware version 0x350f02)
psmouse serio1: elantech: Synaptics capabilities query result 0xb9, 0x15, 0x0c.

Signed-off-by: Ulrik De Bie <ulrik_opensource-kernel@yahoo.com>