draw: don't run pipeline stages when gs has no position output

The clip stage may crash if there's no position output, for this reason
code was added to avoid running the pipeline stages in this case
(c7c7186045ec617c53f7899280cbe12e59503e4d). However, this failed to actually
work when there was a geometry shader, since unlike the vertex shader it did
not initialize the position output to -1, hence the code trying to detect
this didn't trigger. So simply initialize the position output to -1 just like
the vs does.
This fixes piglit glsl-1.50-transform-feedback-type-and-size (segfault->pass).
clip-distance-out-values.shader_test goes from segfault to assertion failure,
suggesting more fixes are needed, no other piglit changes.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
draw: fix clipvertex trouble if position comes from gs

If the vertex shader has no position but the gs has, the clipvertex output
was -1 (because it's the same as vs position in this case if there's no
explicit clipvertex output). This caused crashes (or assertion failures) in
clipping since in the end position (which came from gs) was different from
cv (-1) and we then tried to use the bogus cv input.
Rather than just test for -1 cv value in clipping, make it explicitly return
the position output of the gs instead which seems cleaner (since we really
don't want to use the clipvertex value from the vs (it could be a valid value
in the (unsupported) case of vs writing clipvertex but still using a gs).
This fixes piglit shader_runner clip-distance-out-values.shader_test.

Reviewed-by: Zack Rusin <zackr@vmware.com>
mesa/formats: Use the correct swizzle parameter for the 11-bit EAC formats

Red-only formats should be x001 and RG formats should be xy01.

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
mesa/formats: Fix the size of ETC2_SRGB8_PUNCHTHROUGH_ALPHA1

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>