psmouse: Add some support for the FocalTech PS/2 protocol extensions.

Most of the protocol for these touchpads has been reverse engineered. This
commit adds a basic multitouch-capable driver.

A lot of the protocol is still unknown. Especially, we don't know how to
identify the device yet apart from the PNP ID. The code currently compares
known good values with all data from the touchpad which could be usable for
identification, so by design even minor variations will cause the driver
to fail to detect the device and fall back to compatibility mode.

The previous workaround for these devices has been left in place in case
the driver is not compiled into the kernel or in case some other device
with the same PNP ID is not recognized by the driver yet still has the same
problems with the device probing code.