fix(display): Tweaks to memory Kconfig settings.

* Don't default heap mempool by default now that there's a dedicated
  LVGL mempool
* Set proper defaults for CiZ display hardware/custom screen.
* Double the dedicated display thread stack size for CiZ.

app/module/drivers/display/il0323.c

@@ -177,6 +177,7 @@ static int il0323_clear_and_write_buffer(const struct device *dev, uint8_t patte
 
     line = k_malloc(IL0323_NUMOF_PAGES);
     if (line == NULL) {
+        LOG_ERR("Failed to allocate memory for the clear");
         return -ENOMEM;
     }