anv: Emit CS stall on INTEL_MEASURE timestamp

anv: Emit CS stall on INTEL_MEASURE timestamp

For INTEL_MEASURE, ensure all prior instructions completed before
timestamp taken. Continue to support no CS flush case for Perfetto.
CS stall was dropped from pipecontrol when adding u_trace support.

Fixes: cc5843a573b ("anv: implement u_trace support")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20502>