radv: allow applications to dynamically change RADV_FORCE_VRS

radv: allow applications to dynamically change RADV_FORCE_VRS

This introduces inotify support in RADV to handle changes from the
RADV_FORCE_VRS_CONFIG_FILE. This is similar to MangoHUD. I'm personally
not sure it's the best solution but let's try this way and change it
later if we have issues (or if we have a lightweight solution).

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14713>