Input: add OLPC AP-SP driver

The OLPC XO-1.75 and XO-4 laptops include a PS/2 touchpad and an AT
keyboard, yet they do not have a hardware PS/2 controller. Instead, a
firmware runs on a dedicated core ("Security Processor", part of the SoC)
that acts as a PS/2 controller through bit-banging.

Communication between the main cpu (Application Processor) and the
Security Processor happens via a standard command mechanism implemented
by the SoC. Add a driver for this interface to enable keyboard/mouse
input on this platform.

Original author: Saadia Baloch
Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>