doc: input: add a list of general purpose drivers

Add a list of general purpose input drivers, hopefully this will make
them easier to be discovered by users.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

doc/services/input/index.rst

@@ -86,8 +86,28 @@ compatibility device node, for example:
         };
     };
 
-Driver Documentation
+General Purpose Drivers
-********************
+***********************
+
+- :dtcompatible:`adc-keys`: for buttons connected to a resistor ladder.
+- :dtcompatible:`analog-axis`: for absolute position devices connected to an
+  ADC input (thumbsticks, sliders...).
+- :dtcompatible:`gpio-kbd-matrix`: for GPIO-connected keyboard matrices.
+- :dtcompatible:`gpio-keys`: for switches directly connected to a GPIO,
+  implements button debouncing.
+- :dtcompatible:`gpio-qdec`: for GPIO-connected quadrature encoders.
+- :dtcompatible:`input-keymap`: maps row/col/touch events from a keyboard
+  matrix to key events.
+- :dtcompatible:`zephyr,input-longpress`: listens for key events, emits events
+  for short and long press.
+- :dtcompatible:`zephyr,lvgl-button-input`
+  :dtcompatible:`zephyr,lvgl-encoder-input`
+  :dtcompatible:`zephyr,lvgl-keypad-input`
+  :dtcompatible:`zephyr,lvgl-pointer-input`: listens for input events and
+  translates those to various types of LVGL input devices.
+
+Detailed Driver Documentation
+*****************************
 
 .. toctree::
    :maxdepth: 1