modules: lvgl: add zephyr,lvgl-pointer-input pseudo device

Add the scaffolding to create input lvgl pseudo devices which route zephyr
input_event to their lvgl `indev` equivalent. As a first cut also add a
`zephyr,lvgl-pointer-input compatible which can be a drop-in replacement
for the existing kscan solution.

Signed-off-by: Fabian Blatz <fabianblatz@gmail.com>