HID: asus: Add i2c touchpad support

Update the hid-asus module to add multitouch support for the Asus i2c touchpad.

This patch aims to resolve the issue raised here:
https://bugzilla.kernel.org/show_bug.cgi?id=120181

The issue is in relation to an Asus touchpad device which currently does not
have multitouch support.

The device currently falls through to the hid-generic driver which
treats the device as a mouse.

This patch aims to add the multitouch support.

[jkosina@suse.cz: move most of the 'patch comment' into actual changelog]
[jkosina@suse.cz: drop hunk that changes ->name of the driver]
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Brendan McGrath <redmcg@redmandi.dyndns.org>
Signed-off-by: Victor Vlasenko <victor.vlasenko@sysgears.com>
Signed-off-by: Frederik Wenigwieser <frederik.wenigwieser@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>