glsl: pass shader stage to lower_output_reads and handle tess control

glsl: pass shader stage to lower_output_reads and handle tess control

Tessellation control outputs can be read in directly without first
having been written. Accessing these will require some special logic
anyways, so just let them through.

V2: Never lower tess control output reads, whether patch or not -- both
can be read back by other threads.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>