r600g: add support for primitive id without geom shader (v2)

r600g: add support for primitive id without geom shader (v2)

GLSL 1.50 specifies a fragment shader may have a primitive id
input without a geometry shader present.

On r600 hw there is a special GS scenario for this, you have
to enable GS_SCENARIO_A and pass the primitive id through
the vertex shader which operates in GS_A mode.

This is a first pass attempt at this, and passes the piglit
tests that test for this.

v1.1: clean up debug print + no need to assign
key value to setup output.
v2: add r600 support

Reviewed-by: Glenn Kennard <glenn.kennard@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>