Input: sur40 - add additional reverse-engineered information

Due to recent reverse engineering efforts, a lot more information is now
available about the internals of the SUR40. We document this in the kernel
driver for future use.

Signed-off-by: Martin Kaltenbrunner <modin@yuri.at>
Signed-off-by: Florian Echtler <floe@butterbrot.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>