st/nine: Correctly handle when ff vs should have no texture coord input/output

st/nine: Correctly handle when ff vs should have no texture coord input/output

Previous code semantic was:

. if ff ps will not run a ff stage, then do not output texture coords for this stage
for vs
. if XYZRHW is used (position_t), use only the mode where input coordinates are copied
to the outputs.

Problem is when apps don't give texture inputs. When apps precise PASSTHRU, it means
copy texture coord input to texture coord output if there is such input. The case
where there is no texture coord input wasn't handled correctly.

Drivers like r300 dislike when vs has inputs that are not fed.

Moreover if the app uses ff vs with a programmable ps, we shouldn't look at
what are the parameters of the ff ps to decide to output or not texture
coordinates.

The new code semantic is:

. if XYZRHW is used, restrict to PASSTHRU
. if PASSTHRU is used and no texture input is declared, then do not output
texture coords for this stage

The case where ff ps needs a texture coord input and ff vs doesn't output
it is not handled, and should probably be a runtime error.

This fixes 3Dmark05, which uses ff vs with programmable ps.

Reviewed-by: Tiziano Bacocco <tizbac2@gmail.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>