modules: lvgl: add automatic lv_timer_handler call

inside of its own thread when user enable it on
the LVGL Zephyr options menu, using this option makes
the calling of the lv_timer_handler driven by an internal
timer and thread. Options like priority and stack size
for this thread are exposed making it configurable by the
application.

Signed-off-by: Felipe Neves <ryukokki.felipe@gmail.com>

modules: lvgl: put LVGL core into a dedicated workqueue

Replacing the initial approach based on timers and semaphore

Signed-off-by: Felipe Neves <ryukokki.felipe@gmail.com>