Hi @newsparky
I have no clue about lvgl and lv_conf.h but this post might help you: Problem with "PROJECT_DIR" variable - #6 by maxgerhardt
So with the following build flags in your platformio.ini this should allow you simply put the lv_conf.h into your src folder.
build_flags =
-Isrc/
-DLV_CONF_INCLUDE_SIMPLE