anv: Flush caches prior to PIPELINE_SELECT on all gens

anv: Flush caches prior to PIPELINE_SELECT on all gens

The programming note that says we need to do this still exists in the
SkyLake PRM and, from looking at the bspec, seems like it may apply to
all hardware generations SNB+.  Unfortunately, this isn't particularly
clear cut since there is also language in the bspec that says you can
skip the flushing and stall to get better throughput.  Experimentation
with the "Car Chase" benchmark in GL seems to indicate that some form of
flushing is still needed.  This commit makes us do the full set of
flushes regardless of hardware generation.  We can always reduce the
flushing later.

Reported-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: "17.0 13.0" <mesa-stable@lists.freedesktop.org>