Input: goodix-berlin - add sysfs interface for reading and writing touch IC registers

Input: goodix-berlin - add sysfs interface for reading and writing touch IC registers

Export a sysfs interface that would allow reading and writing touchscreen
IC registers. With this interface many things can be done in usersapce
such as firmware updates. An example tool that utilizes this interface
for performing firmware updates can be found at [1].

[1] https://github.com/goodix/fwupdate_for_berlin_linux

Signed-off-by: Charles Wang <charles.goodix@gmail.com>
Link: https://lore.kernel.org/r/20240514115135.21410-1-charles.goodix@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>