modules: lvgl: add missing stubs for Kconfig symbols

Add missing `LV_Z_HOR_RES_MAX`, `LV_Z_VER_RES_MAX`
and `LV_Z_DISPLAY_DEV_NAME`
Kconfig symbols to fix the following Kconfig warnings:

warning: LV_Z_DISPLAY_DEV_NAME defined without a type
warning: LV_Z_HOR_RES_MAX defined without a type
warning: LV_Z_VER_RES_MAX defined without a type

Fixes
Signed-off-by: Bartosz Bilas <b.bilas@grinn-global.com>