renderer: use per-sampler dirty flags

This tracks more accurately what exactly needs to be updated.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
7 jobs for sampler-optimize in 86 minutes and 21 seconds (queued for 18 seconds)