Input: rotary-encoder - update docs according to the latest API changes

The old device property API is about to be removed, so
explaing how to use complete software nodes instead.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20210304090948.27014-1-heikki.krogerus@linux.intel.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Input: docs - use PROPERTY_ENTRY_U32() directly

Instead of using PROPERTY_ENTRY_INTEGER() with explicitly supplied type,
use PROPERTY_ENTRY_U32() dedicated macro.

It will help modify internals of built-in device properties API.

No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Input: docs - split input docs into kernel- and user-facing

Split input documentation into several groups: kernel- and user-facing, and
notes about individual device drivers. Move device drivers docs into a
separate subdirectory.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>