tgsi: keep track of read vs written indirects

tgsi: keep track of read vs written indirects

At least temporarily, I need to fallback to old compiler still for
relative dest (for freedreno), but I can do relative src temp.  Only
a temporary situation, but seems easy/reasonable for tgsi-scan to
track this.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>