Input: sentelic - document the latest hardware

- Add documentation for the Cx/Dx hardware release;
- Fix wrong register offset for retrieving button information;
- Document programming sequence for page register R/W;
- Document a couple of supported gesture IDs.

Signed-off-by: Tai-hwa Liang <avatar@sentelic.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>