i965: Don't set the "switch" flag on control flow instructions on Gen6+.

i965: Don't set the "switch" flag on control flow instructions on Gen6+.

Thread switching on control flow instructions is a documented workaround
for Gen4-5 errata.  As far as I can tell, it hasn't been needed since
Sandybridge.  Thread switching is not free, so in theory this may help
performance slightly.

Flow control instructions with the "switch" flag cannot be compacted, so
removing it will make these instructions compactable.  (Of course, we
still have to implement compaction for flow control instructions...)

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>