Input: byd - add BYD PS/2 touchpad driver

Driver for the BYD BTP10463 touchpad, found in PC Specialist `Lafite'
laptops. This patch sends the magic command sequence which causes the
touchpad to stream intellimouse-style packets.

Gestures are detected inside the touchpad, and exposed as special
values in the Z component of each packet - absolute coordinates are
not supported, even in the Windows driver. At present, this supports
two-finger vertical and horizontal scrolling, and provides the
framework to expose the other gestures it can recognize.

Signed-off-by: Chris Diamand <chris@diamand.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>