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/boards/arm/corneish_zen/Kconfig.defconfig

@@ -57,6 +57,13 @@ config IL0323
 config ZMK_DISPLAY_BLANK_ON_IDLE
     default n
 
+# Needed for the IL0323 driver which allocs memory to clear the display
+config HEAP_MEM_POOL_SIZE
+    default 1024
+
+ config LV_Z_MEM_POOL_SIZE
+     default 4096
+
 endif # ZMK_DISPLAY
 
 menuconfig CUSTOM_WIDGET_BATTERY_STATUS